A sure way to start an argument between boxing and mixed martial arts fans is to ask one simple question.

"What if?"

What if a top mixed martial artist stepped in the boxing ring to take on a world-class boxer? Or what if the boxer stepped in the Octagon?

It's an argument as old as combat sports itself. Before MMA sprang to life in the 1990s, the debate raged between boxing and pro wrestling fans. Which sport had the toughest athletes?

Promoters tried to capitalize on the discussion—most notably with the debacle between Muhammad Ali and Antonio Inoki in 1976—but the scripted environment of pro wrestling offered few answers.

Now, with the upcoming boxing match between Floyd Mayweather Jr. and Conor McGregor, fans finally have their first opportunity to see high-level fighters from both sports facing off.

To celebrate Mayweather vs. McGregor's "fantasy turned reality" vibe, we're going to name seven other dream boxing vs. MMA fights we wish we could've seen.

Anthony Johnson vs. Bobby Gunn

ANTHONY JOHNSON

MMA RECORD: 22-6 (16 KO)
ACTIVE: 2006-2017

BOBBY GUNN

BOXING RECORD: 23-7 (20 KO)
ACTIVE: 1989-2017

Irish Traveller Bobby Gunn isn't the best boxer in the world. In fact, he's known more for his presence on the bare-knuckle fighting circuit than in proper boxing rings. But he packs a mean punch and tends to find himself involved in brutal wars.

Which is why he's the ideal opponent for the headhunting Anthony Johnson, a man with a perfectly reasonable claim to being the most terrifying knockout artist (and most terrifying medicinal marijuana executive) in UFC history.

Oscar De La Hoya vs. Nick Diaz

NICK DIAZ

MMA RECORD: 26-9 (13 KO)
BOXING RECORD: 1-0
ACTIVE: 2001-2015

OSCAR DE LA HOYA

BOXING RECORD: 39-6 (30 KO)
ACTIVE: 1992-2008

The age-old combat sports idiom says styles make fights. This matchup is the perfect illustration of a potentially thrilling fan-friendly action bout.

Diaz is at his very best when paired with an opponent like De La Hoya. Despite his black belt in jiu-jitsu, Diaz appears to be at his happiest when he's being paid huge sums of money to fight an opponent who will stand and trade punches with him. It's one of the traits that helped make him one of the most popular mixed martial artists in the world.

Neither man gives any quarter to the person standing across the cage or ring from him. Both men established themselves as warriors with the highest levels of fighting spirit. De La Hoya, in particular, captured a generation of boxing fans with his unwillingness to surrender, starting with the 1992 Olympics when the boxer fulfilled the wishes of his dying mother by winning a gold medal.

And needless to say, the buildup to the bout would likely be even more exciting than the fight itself.

Anderson Silva vs. Roy Jones Jr.

ANDERSON SILVA
MMA RECORD: 34-8 (20 KO)
BOXING RECORD: 1-1 (1 KO)
ACTIVE: 1997-PRESENT

ROY JONES JR.
BOXING RECORD: 65-9 (47 KO)
ACTIVE: 1989-2017

This one actually came close to becoming reality and still bubbles to the surface every once in a while, but Silva lacked the stardom of McGregor and the UFC wasn't interested in letting its top fighter compete in a boxing ring.

The world wouldn't have taken to Silva vs. Jones the way it has to Mayweather vs. McGregor. But it might've been a far more interesting fight than the one we're getting August 26.

Stipe Miocic vs. Anthony Joshua

STIPE MIOCIC
MMA RECORD: 17-2 (13 KO)
ACTIVE: 2010-PRESENT

ANTHONY JOSHUA
BOXING RECORD: 19-0 (19 KO)
ACTIVE: 2013-PRESENT

The current UFC heavyweight champion hasn't been shy about his desire to box Joshua, who won a slice of the scattered heavyweight title with a knockout of Wladimir Klitschko earlier this year, in a theoretical big-money fight.

Miocic is a very good boxer for someone who competed solely on the amateur ranks in boxing. Still, in a boxing ring, Joshua reigns supreme as the baddest man on the planet. He has racked up gold and championships in a way few heavyweights over the past 20 years have, and he'd be far too much for Miocic to handle. But Miocic would probably last longer than Joshua would in a cage, at least, so there's that.

Roberto Duran vs. Cody Garbrandt

CODY GARBRANDT
MMA RECORD: 11-0 (9 KO)
ACTIVE: 2012-PRESENT

ROBERTO DURAN
BOXING RECORD: 103-16 (70 KO)
ACTIVE: 1968-2001

If you like all-action fights, this is the one for you.

Duran, the Panamanian brawler, became a combat legend for his technique and style, but above all it was his heart that set him apart from his peers. That's if you discount the controversial "No Mas" fight against Sugar Ray Leonard, of course.

Garbrandt is the UFC's bantamweight champion, but he's still young in his career and has much ahead of him, and he looks disturbingly younger with his new creeper mustache. Still, he has traces of Duran in his mixed martial arts style, and he has a lengthy amateur boxing resume.

Fedor Emelianenko vs. Mike Tyson

MIKE TYSON
BOXING RECORD: 50-6 (44 KO)
ACTIVE: 1985-2005

FEDOR EMELIANENKO
MMA RECORD: 36-5 (11 KO)
ACTIVE: 2000-PRESENT

During his murderous run in the 2000s, Fedor Emelianenko drew constant comparisons to Mike Tyson, and this dream fight is one of the few consistently brought to the surface by MMA fans asked to name their wish list of unfulfilled fights.

Emelianenko often blitzed his opponents early, finishing them before they could even get their feet under them. It was more than reminiscent of a young Tyson, who terrified heavyweights (and the world) before finally losing to Buster Douglas in 1990. In a ring or a cage, this one would be violent, bloody and quick.

Muhammad Ali vs. Jon Jones

MUHAMMAD ALI
BOXING RECORD: 56-5 (37 KO)
ACTIVE: 1960-1981

JON JONES
MMA RECORD: 23-1
ACTIVE: 2008-2017

The two greatest fighters in the history of their respective sports.

Yes, Ali was a heavyweight fighter, and Jones is a light heavyweight. But Jones' walking weight is close enough to Ali—and Jones is likely on the verge of a heavyweight move anyway—that we're comfortable pulling the trigger on this.

And really, is there a more perfect boxing vs. MMA dream fight? There is not. The GOAT vs. the GOAT is the ultimate boxing vs. MMA fantasy. Jones is clearly inspired by Ali, even using Ali's "the champ is here" catchphrase to drive the beat of his UFC entrance music. Jones is essentially undefeated over a 24-fight career; few observers or fans of the sport count his disqualification loss to Matt Hamill as a blight on his perfect record.

Apologies to Floyd Mayweather and Conor McGregor, but this is the ultimate boxing vs. MMA dream fight.