If the middle of March seems like a strange time to start thinking about 2019 NBA free agency, consider a couple of important points.

First, the transactional side of the NBA news cycle is of greater interest than ever. For example, we're as likely to remember the Anthony Davis trade/no-trade saga as clearly as James Harden's historic scoring run when we reminisce about the 2018-19 season.

Second, with all but a couple of playoff spots decided, nearly half the league is already shifting its focus from this year to next. And that means the draft and free agency are suddenly top priorities.

If anything, we've waited too long to rank top free agents.

The criteria are simple. The best player is the one who'd make the biggest positive difference if he signed with your team. The guy in second would make less of an impact than the player ranked below, and so on. In the interest of completeness, we've included free agents of all stripes—from unrestricted to those holding player options.

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A few quick honorable mentions before we get to the top 25. We owe Thaddeus Young, Derrick Rose, Jeff Teague, Ricky Rubio and Bobby Portis the courtesy of a nod. We had to draw the line somewhere, and these five fell on the wrong side of it.

25. Jonas Valanciunas, Memphis Grizzlies, Player Option

The market for conventional centers has declined enough since he signed his last deal that Valanciunas should expect annual rates on his next one to be around half of the $17.6 million player option he's got for 2019-20. The 26-year-old has enjoyed a production spike with the Grizzlies, but bigs who don't stretch the floor or change the game on defense just aren't in high demand as starters—not even ones with career averages of 11.9 points and 8.4 rebounds.

24. Terry Rozier, Boston Celtics, Restricted

The version of Rozier that outplayed Eric Bledsoe in the first round of the 2018 playoffs and hunted big shots throughout the postseason is a starting NBA point guard worth upward of $15 million per season. The one who's shot under 40 percent from the field in each of his four years with the Celtics is a spark plug backup.

Buyers will have to decide which one they think is real.

23. Malcolm Brogdon, Milwaukee Bucks, Restricted

Brogdon is a month away from finishing a 50-40-90 season and has strung together three straight years in which he's ranked in or above the 85th percentile at his position in points per shot attempt. He's not a pure point guard, and quicker opponents can get by him on the perimeter, but Brogdon offers exceptionally efficient mid-volume offense, smarts and high character as a top-notch role player.

22. Goran Dragic, Miami Heat, Player Option

It's easy to forget Dragic was an All-Star in 2017-18, and his on-off splits show he's improved the Heat's offensive efficiency by at least three points per 100 possessions in every season with the franchise. It's not a stretch to say he's been the most important Heat player in the half-decade since LeBron James left.

Heading into his age-33 season, Dragic is coming off the first injury-hit campaign of his career. Until this year, he hadn't missed more than 10 games in a season since 2010-11...when he missed 12. If he can be counted on for another 70 contests, this ranking will be way too low.

21. Nikola Mirotic, Milwaukee Bucks, Unrestricted

A more complete player than most think (Mirotic is in positive territory in DRPM, and the Pelicans defended better with him on the floor before dealing him to the Bucks), Mirotic is one of three players averaging over 2.5 made threes and seven boards this season. Paul George and Kevin Love are the others.

His value is still tied mostly to floor-stretching at the 4, but Mirotic can contribute solid post defense when he's cold from outside. At worst, he's a good third option who can break games open with hot streaks and won't turn 28 until after next year's trade deadline.

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20. Paul Millsap, Denver Nuggets, Team Option

Millsap missed 13 games in his last All-Star season with the Hawks, 44 in his first year with Denver and will top out at 71 in the unlikely event he suits up for every contest over the balance of 2018-19. He's still a dirty-work superstar and proverbial glue guy—one who can elevate a team without necessarily wowing with box score stats. And his per-minute scoring and rebounding rates this year are right in line with his career averages.

But at age 34, Millsap may be transitioning to the phase of his career where he can't be deployed for more than the 26.7 minutes per game he's playing this year. That and the looming possibility of a steep age-related decline make him a high-risk, high-reward play...if Denver turns him loose by declining its $30 million team option.

19. Julius Randle, New Orleans Pelicans, Player Option

Randle's breakout year, fueled by growth as a shooter (he's now passable from deep after being a total non-threat in his first four seasons) and a relentless attacking mentality, makes him an intriguing free-agent option. Maybe his defensive shortcomings limit his impact on team success, but there's no way a 24-year-old averaging over 20 points per game on decent efficiency would opt in for $9.1 million.

He'll hit the market with a good shot to collect twice that much per season on a multiyear deal, and another slight improvement from deep would make him one of the more complete offensive bigs in the league.

18. JJ Redick, Philadelphia 76ers, Unrestricted

There aren't many one-dimensional, one-way players who make the difference Redick does. His incessant sprinting around screens, give-and-go-and-give-again synergy with Joel Embiid and unmatched ability to go from a dead run to a balanced shooting posture make him a genuine defense-breaker.

Redick's averaging a career high in scoring during his age-34 season, a testament to his conditioning and ability to make difficult shots. He ranks this low because smart playoff opponents target him on D, and because age is a concern. Maybe he can sustain this level, but the odds decrease every year. 

17. Danny Green, Toronto Raptors, Unrestricted

A low-usage three-and-D role player, Green remains one of the most desirable supplemental pieces in the league. Though his block and steal rates are down this year from their typical elite levels, both remain above average for the wing position. Capable of harassing point guards and holding up against all but the biggest wings on defense, the 31-year-old Green is an ideal fit on any team that's serious about winning games.

He's not as dynamic offensively as Redick, but Green is a 40 percent career shooter from deep and has been the more accurate of the two this year. And the defensive comparison is no contest.

16. DeMarcus Cousins, Golden State Warriors, Unrestricted

Cousins couldn't lead the Sacramento Kings to the playoffs as their focal point, but organizational dysfunction contributed to his lack of success. Then, the Pelicans got better and won a playoff series after he went down with a torn Achilles in 2017-18. With the Warriors, Cousins' understandably compromised post-injury mobility has exacerbated his defensive deficiencies. 

The frustration fouls, slow jogs in transition and bad body language persist.

BUT!

Cousins is undeniably one of the most skilled and physically gifted bigs in the league, and he's had seasons of monstrous statistical production. In theory, he should be better the further removed he is from his Achilles surgery.

Roll all that together, and you've got a guy who could be ranked 10 spots higher or excluded from the top 25 entirely. He lands here because we're throwing our hands up and splitting the difference.

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15. Brook Lopez, Milwaukee Bucks, Unrestricted

Lopez isn't a star in the conventional sense, but he's exceptionally valuable because he's so good at the finite number of things he's asked to do. He is currently on pace to average over six three-point attempts and two blocks per game, something no player has ever done before. His ability to stretch defenses well beyond the arc (Lopez takes some deeeeeeeep threes) and defend the rim in drop coverage is key to Milwaukee's dominant play on both ends. The Bucks offense scores at a rate that would rank second in the league with him on the floor but drops to a bottom-five clip without him.

Not every team will employ Mike Budenholzer's schemes, which maximize Lopez's skills, but rim defense and floor-stretching will always be in high demand.

14. Marc Gasol, Toronto Raptors, Player Option

Gasol is 34 and may be transitioning to the role of part-time starter from here on, but if you don't trust him to be a more consistent across-the-board contributor than Cousins next year, you're out of touch with reality.

A sturdy post defender who's now strung together three years of serviceable shooting beyond the arc, Gasol is still a terrific passer and communicator. He can run an offense for long stretches, and he makes up for declining mobility with anticipation and positioning. He can't hang with mobile 5s or switch onto guards, but neither can any of the centers ranked below him.

13. Bojan Bogdanovic, Indiana Pacers, Unrestricted

All Bogdanovic has done this year is transition seamlessly from Victor Oladipo's sidekick to one of the most effective and efficient wings in the league, proving he's up to the task of high-usage play as a focal point on a playoff-bound team.

The 29-year-old averaged 23.1 points per game on 64.5 percent true shooting in February and is keeping the Pacers in position for a top-four seed during March. Maybe he's limited defensively, but Bogdanovic embraces the challenge of guarding top wings, and he competes on both ends. That we've made it this far without mentioning he's one of only nine players shooting over 42 percent on at least 300 long-range attempts this season says a great deal about his value.

A standstill shooter on the level of Green and Redick, Bogdanovic can also create his own looks in ways those two can't.

12. D'Angelo Russell, Brooklyn Nets, Restricted

Russell struggles to get to and finish at the rim, and he's got a long way to go as a foul-drawer. But he makes up for those shortcomings with extreme craft in the pick-and-roll and a dangerous pull-up game from deep.

With an All-Star berth in his age-22 season, the former No. 2 draft pick profiles as a true first-option point guard—one who can generate reasonably efficient offense with an extreme usage rate. Maybe we should bake in some regression after a breakthrough season, but given Russell's feel for the game, demonstrated shot-making and youth, it's hard to be bearish about his future value.

11. Kristaps Porzingis, Dallas Mavericks, Restricted

Franchise-altering upside and terrifying injury risk collide here, making for one of the trickier subjects to rank on our list.

There aren't any other 7'3" bigs with Porzingis' guard skills, track record of sterling rim defense and feathery stroke. But in addition to concerns about his comeback from a torn ACL, there's also the fact that his production consistently trends downward over the course of a season. KP's scoring and rebounding averages, along with his true shooting percentage, are all worse after the All-Star break, and he's played just one career game in the month of April. A catastrophic injury, like a torn ACL, is one thing. But the consistent failure to stay healthy and productive over a six-month span should raise questions about his general durability.

Generally, the October-November edition of Porzingis is a superstar. December through April? Not so much.

10. Khris Middleton, Milwaukee Bucks, Player Option

Solid isn't sexy, but Khris Middleton plays the role of a well-rounded wing as capably as any non-star in the league.

A career 38.8 percent three-point shooter, Middleton has been better than average as a foul-drawer for his position over the last four seasons. Add to that a steal rate that has ranged from good to elite throughout his career and an assist rate that ranks in the 92nd percentile among wings this year, and you've got a 27-year-old free agent (28 in August) with no exploitable weaknesses.

And if availability is the most important ability, Middleton's value only increases. Outside of a torn hamstring that cost him 53 contests in 2016-17, he hasn't missed more than three games in a season since his rookie year.

Maybe the known-commodity status means Middleton's ceiling isn't as high as some of the players' ranked below him. But there's something to be said for high floors, too.

9. Tobias Harris, Philadelphia 76ers, Unrestricted

It took him seven-plus seasons and five teams, but Tobias Harris made himself into a top-notch second option. Considering the growth he's shown to this point, who's to say his trajectory will stop there?

Harris may not have the high-end 2019-20 value of the guys ranked ahead of him, but he's likely to age better than most of them. Still only 26, he's played at least 76 games in each of his last three completed seasons and hasn't missed one yet this year. Durability and a steady track record of improvement may not trigger thoughts of stardom, but don't be surprised when the Sixers either match four-year max offer sheets from competitors or add a fifth season to retain their sweet-shooting forward.

After hitting 41.1 percent of his treys in 2017-18, Harris has been even better than that this year and is one of just six players averaging over 20 points while shooting above 40 percent from deep this year.

Outside of marginally negative defensive impact, Harris is a sound investment for a team in need of a No. 2 option.

8. Nikola Vucevic, Orlando Magic, Unrestricted

Nikola Vucevic is the only player, free agent or otherwise, currently averaging over 20 points, 12 rebounds, 3.5 assists and one made three per game.

The Orlando Magic are generally poor on offense, but they collapse whenever Vucevic doesn't play, tumbling to an offensive rating over six points per 100 possessions worse than the league's least efficient team. The very worst you can say about Vooch's offensive impact this season is that he's been a phenomenal floor-raiser. His presence on the court allows Orlando to survive.

Defensively, the 28-year-old center grades out well. The Magic are better on D when Vucevic plays, and he has positive marks in virtually every catch-all metrics: D-PIPM, DRPM and defensive box plus-minus.

If you only had this season to judge Vucevic, you'd peg him as a franchise-level center. It's just that the first-time All-Star's incredible statistical improvement owes heavily to a spike in three-point accuracy. Mid-career leaps happen, but it seems wise to value Vucevic going forward as a player who'll perform better than he did in his first seven seasons, but not quite as well as he has in his eighth.

Maybe that's an uncharitable way to view one of this season's most productive forces, but a significant sample of sub-star-level play has to temper the expectations brought about by a phenomenal 2018-19 performance.

7. Al Horford, Boston Celtics, Player Option

Al Horford ranks third among free-agent centers in Jacob Goldstein's catch-all Player Impact Plus-Minus and ESPN's Real Plus-Minus, but even at age 32, he's still the most complete option at the position. He's also playoff-tested to a degree Vucevic and Lopez, who rank ahead of him by both metrics, are not.

Those guys can't lay claim to owning Joel Embiid throughout a postseason series, and it's unlikely either of them ever will.

That's because Horford's versatility on both ends is unparalleled among free-agent bigs. He can stretch out to three-point range and attack closeouts on offense. Better still, you can trust him to facilitate as a hub from the elbows. Vucevic is right there with Horford in assists per game this season, but the Magic center's turnover rate is higher. And while Vooch has shot it better from deep in a breakout campaign, his inability to get to the foul line means Horford still owns a higher true shooting percentage.

Horford is showing signs of decline this year. He's battled knee soreness and isn't always as spry on switches as he used to be. All the same, he's a plug-and-play winner who contributes across the board—and has been for a decade. Vucevic's long-range shooting accuracy this year will be an outlier until he repeats it, and though he's probably been underrated defensively for a while now, his reliability on that end isn't on Horford's level.

This was a close call, but if we're talking about level of impact next year, Horford is still the better option.

6. Jimmy Butler, Philadelphia 76ers, Player Option

Maybe this feels too low for Jimmy Butler, a 6'8" wing with four 20-points-per-game seasons and a pair of All-Defense nods to his name. Isn't that player type—the one who can create an efficient look at the end of games after guarding the opponent's best player for 40 minutes—what absolutely everyone wants?

Unfortunately, we have to weigh all that against the baggage Butler brings.

When you tear a team apart from the inside, like Butler did in seeking his exit from the Minnesota Timberwolves, it becomes part of the evaluative picture alongside competitiveness, foul-drawing guile and defensive chops.

Butler will play his age-30 season next year, though it's hard to know how much downside risk to bake in because of all that time playing for Tom Thibodeau. Butler led the league with 38.7 minutes per game in 2014-15 and averaged 15.2 missed contests from 2013-14 to 2017-18. The risk of physical breakdown is probably greater for him than it is for others with similar age-and-mileage profiles.

Probably not worth the max on a long-term deal, Butler is still an All-Star-caliber talent at a position of extreme value. Framed another way, there are four wings ahead of him on this list, and a team should feel pretty good matching him up against any of them in a do-or-die situation.

5. Kemba Walker, Charlotte Hornets, Unrestricted

Until as recently as 2014-15, Kemba Walker was a smallish volume scorer limited by substandard three-point shooting and barely break-even defensive impact. That player is gone now, replaced by a three-time All-Star whose comfort from deep bends defenses much like Stephen Curry, Damian Lillard or your off-the-dribble gunslinger of choice.

Walker is happy to take as many pull-up treys as your defensive scheme will allow, generally to great effect. Only James Harden attempts more such shots per game this season, and though Walker is only hitting them at 35.7 percent (38.1 percent last year), that's still more than accurate enough to rank first on every opposing team's "must not allow" section of the scouting report.

Among high-volume pick-and-roll ball-handlers, only Lillard averages more points per possession than Walker.

Undersized guards who depend on quickness don't often age gracefully, but Walker is averaging a career-high in scoring in his age-28 season. Even if decline begins next year, he'll still be the kind of offensive force around which a team can build its entire scheme. 

4. Klay Thompson, Golden State Warriors, Unrestricted

Klay Thompson, platonic ideal of the three-and-D wing, is the most scaleable non-superstar in the league and quite possibly the most low-maintenance difference-maker you could add to a roster.

If he had any more chill, Thompson would by hypothermic.

His quick-fire sniping requires constant off-ball attention in half-court sets and in transition. Stephen Curry deserves credit for activating the Warriors offense over the last half-decade, but Thompson's presence is what makes things unfair.

If you need high-volume shooting, he's scored 37 points in a quarter. He can get you 40 without dribbling (or 43 points on four dribbles, if you want to be precise about it). He can defend the other team's best offensive player at the 1, 2 or 3 while holding up just fine against most power forwards on switches.

A five-time All-Star who has never shot below 40 percent from three in a season, Thompson fits everywhere and makes everyone better. He won't be a primary shot-generator, but his contributions take teams from good to great on both ends. Still just 29, one of the greatest shooters of all time has plenty of excellent seasons ahead.

3. Kyrie Irving, Boston Celtics, Player Option

Though not the top free agent on our list, Kyrie Irving is definitely the woke-est. Or, at least that's the vibe his public comments seem to convey. Prone to next-level "what's it all mean?" diatribes and curt, emotionally driven responses to (often similar) questions from week to week, Irving can be a bit of a wild card in the leadership department.

His development into the kind of locker room lodestar a contending team needs is ongoing, and his candor and accountability are valuable. But that element lags behind his unquestionably elite offensive performance on the court. Irving's game is that of a clear superstar, while his influence on a team's morale isn't yet similarly verified.

There's nothing wrong with being thoughtful, but a general air of moodiness and unknowability isn't typically associated with stable leadership.

No scorer's bag of tricks is deeper, no ball-handler's breadth of moves is more dangerous and no finisher's creativity is more inspiring. If Irving leads your offense, you've got a chance to beat absolutely anyone. And for what it's worth, he's shown flashes of substantially improved defensive effort this season, grading out in positive territory for the first time in ESPN's Defensive Real Plus-Minus.

A six-time All-Star with a title in the bag and complete confidence in the biggest moments, Irving is as close as we've come to a clear cornerstone so far. 

2. Kawhi Leonard, Toronto Raptors, Player Option

Kawhi Leonard's durability—he still hasn't played both ends of a back-to-back this season after missing 73 games a year ago—remains in question. If his quad injury is of the degenerative variety, it may be unwise to commit long-term money to a player whose future health could be compromised.

Fortunately for potential Leonard buyers, the production he provides when available makes his periodic rest worth the hassle. Leonard is one of four players—joining Giannis Antetokounmpo, James Harden and Stephen Curry—posting a usage rate over 30 percent and a true shooting percentage north of 60 percent this season. For someone with a pair of Defensive Player of the Year awards, that level of high-volume offensive efficiency is hard to fathom.

The two-way label gets overused, and Leonard isn't the consistent stopper he once was, but it's awfully hard to find a player who can dominate both ends like he can.

Heading into his age-28 season, Leonard, like Kevin Durant, is capable of being the best player on a title-winning team. That's not something you can comfortably say about anyone ranked lower on this list.

1. Kevin Durant, Golden State Warriors, Player Option

Kevin Durant is showing no signs of slippage in his age-30 season, and there's little reason to expect decline anytime soon. His length and shooting touch mean he'll be an elite scorer deep into his 30s.

One of just three players (Wilt Chamberlain and LeBron James are the other two) to own career averages of at least 27 points per game with an effective field-goal percentage above 54 percent, Durant is a true all-timer. He's got an MVP, two rings, four scoring titles and eight All-NBA selections...so far.

If you want to pick nits in his game, Durant's three-point percentage is lower this season than it's been since 2010-11. Of course, he makes up for it with elite efficiency from mid-range, at the rim and at the foul line.

One potential point of caution for the especially wary suitor: Durant has been a little bristly ahead of free agency. If a team signs him to a short-term deal, it should expect KD to be similarly annoyed by questions about his future. There's also the consistent mystery about what he wants from his career. If someone can't be fully content putting up numbers and chasing titles with the Warriors, what possible scenario could produce greater happiness?

Unless otherwise noted, stats courtesy of NBA.com, Cleaning the Glass or Basketball Reference and accurate through games played Thursday, March 14. Salary and cap-hold information via Basketball Insiders.