I guess it depends on which P4P ranking you're referring to.
Personally, if you ask me, I think Floyd should be #1 simply because, I don't see how any fighter at any weight can beat him. Not knocking Manny or anything, because I think Manny's a great fighter as well, but I've seen Manny beaten before...I've seen Manny get touched up and come close to losing before...recently as a matter of fact. If we're talking pound for pound, then hypothetically speaking, if Manny were fighting at 175 pounds and faced a guy like Hopkins, I think he's got some holes in his game that Hopkins would be able to exploit. On the other hand, if Mayweather were fighting at 175 pounds and faced Hopkins, I think Bernard would have an EXTREMELY difficult time landing any of the 10 punches he throws each round. If we're strictly talking about a guy who could potentially beat anyone at any weight he fights at, I'd have to say that at this point, Floyd fits the bill moreso than Manny. Again, that's not to say that Manny ain't a bad mofo either...I just think when he fights slick boxers or guys that counterpunch effectively, he has problems. That doesn't mean he can't win, but it does mean that he has some holes in his game that can be exploited. In my opinion, it's extremely difficult to find holes in Floyd's game...especially considering that he's never been beat and he's never really even come close to being in serious danger of losing a fight. I guess those that would argue that point will talk about the his first fight with Castillo, but still, that was 7 years ago...meanwhile, I just saw Pacquiao struggle and win just as "controversial" of a decision against Marquez just 15 months ago.
Just my opinion...but truthfully, I'm not reall a big fan of P4P lists anyway. They're really meaningless. I mean, technically speaking, I think either one of the Klitschko brothers should probably be listed in the top 5 and yet, they're not. I mean, if we're talking pound-for-pound, I'd have to assume that both brothers would still enjoy the same physical advantages (height, reach, strength, etc.) over their opponents if they were fighting at heavyweight or lightweight and if that's the case, I think there's a lot of guys that would have an EXTREMELY difficult time getting around their jabs...Shane Mosley would probably be eating those Klitschko jabs all night. LOL.