(Names link to highlights)
Pernell "Sweet Pea" Whitaker(40(17 KO's)-4-1-1 NC) 
VS.
Floyd "Money" Mayweather(40(23 KO's)-0-0)
Too me this would be the greatest defensive fight in boxing history. The 2 best defenses in the game. Floyds is the best in terms of defending himself and being able to not get hit. But Pernell's opened up alot more offense and it was more effective in the fight. It wasn't about just not getting hit, it was about making your opponents pay 2. And even though Pernell got hit more(Even though that tends to happen when you actually fight the elite guys in YOUR weight class unlike Floyd), he made you pay more then Floyd does. Both are sickly fast. Floyd has more power IMO, but Pernell was way more active as I stated above. Pernell fought for the fans, Mayweather fights for the money.
Also it should be mentioned Pernell really was in most opinions, as well as mine undefeated at 44-0 until he fought Trinidad past his prime and he even fought 6 rounds with a broken jaw. His last win was a NC for cocaine posession, but in a #1P4P vs #2P4P fight against Julio Cesar Chavez(87-0 at time), he school Chavez and got robbed with a draw. One of the biggest screwjobs in boxing. Also against Jose Luiz Ramirez he lost a split decision when he was schooling him the whole time and got a BS loss in France, but avenged it a year later in the US when he school him again in
One of the greatest displays of defensive boxing I have ever seen!!!(1st fight in video) Not to mention a lot of people thought he beat A PRIMED Oscar De La Hoya too. Elected to the Boxing Hall of Fame a champion in 4 different weight classes. Floyd also has been a champ in several different weight classes, 4 or 5. At the lighter weights he fought the best offered and beat them but since coming up to welterweight that all changed as he has yet to fight someone his size like Cotto, Mosely, or Clottty, or even Paul Williams(Not exactly his size hahaha) but instead looks for JMM & Pacman.
Who do you think would win this fantasy fight? Very interesting fight but just because his defense helped his offense be very more effective and set up openings and because he was more active I'd take Pernell in an extremely close decision that in real life would probably go to Floyd because of how Pernells always robbed haha