It is arguable that one of these guys beat the greatest fighter of all time in their own natural weight division, despite being outweighed, as well. The same guy also beat arguably the greatest 2 fighters of all time in the division below him. In fact he arguably beat 3 of the top 10 pound for pound fighters of all time. Not really sure that the other guy can put up such an argument, can he?
I'd say Marciano. Some of Floyd's fights had been set up to favour him (eg Canelo drained to a husk) and then there's the story of the IV's that raises a few questions. Floyd also avoided guys like Pac until it was obvious they had deteriorated and that they no longer were a stylistic nightmare for him. Marciano fought who he was supposed to fight when he was supposed to fight them.
Floyd. He did fight good fighters much earlier in his career than did Marciano. He wasn't anywhere near as exciting but he did fight at a higher level.
My counter to that is that Marciano was as raw as day-old prosciutto when he started his pro career. He had to basically learn on the fly and flipping quickly.
Floyd.. And it isn't even close. He won a title in only his 18th pro bout and spent the bulk of his career in a championship ring. Won belts in numerous weight classes, beat loads of undefeated guys in their primes and several who were p4p better than anyone Marciano beat or at least at the time he fought them. Frankly I'm surprised anyone would even question it to the extent of starting a thread on the subject.
I would have to say Mayweather. A higher percentage of his fights were against world class opposition, and that is always going to be the bottom line. I have more admiration for Marciano in many ways, because he was absolutely scrupulous in going after the best qualified opposition as champion. But, I have to cast my vote for Mayweather.
It's arguable Corrales is a great SFW but I wouldn't back it personally. Pacquiao might be the greatest in a given division but I'm not sure which one that would be. I do agree that Rocky doesn't have much of an argument at all though. Any resume comparison leaves him in the dust.
canelo offered that weight, got up to the 180's come fight time anyway. pac avoided PED testing because he must have been on PEDS, otherwise he had no reason to avoid testing. ESPN has the whole thing on youtube about pac and testing.
corrales was a great one, but the best ever at ANY weight is incorrect same with pac ...good fighter but not the best ever at any weight. at 35...duran at 22...gomez at 40...pryor at 47... leonard/robinson at 30...arguello so. floyd never beat the best ever in any division he competed at at 54 it was either mccallum or hearns