My .02 cents that no one asked for:

Just read the last paragraph if you want a summary of all this jibber jabber, haha.

(For comparison purposes, I consider RJJs prime ending with the 2nd Tarver fight):
I think most "experts" would put RJJ's career legacy and P4P status ahead of Mayweathers. Although RJJ doesnt have a lot of the elite names on his resume as Floyd does, RJJ did cake walk through 3-divisions in his prime (Middlewight - Light Heavy) while clearing out the top-10 of those divisions. Its just unfortunate that those divisions were really weak in the 90s while RJJ reigned. The only guy I can clearly remember RJJ not fighting is Dariusz Michelewski (I know I probably butchered that spelling). But that was because Dariusz refused to fight outside of Germany. At that time, Germany was notorious for robbing American fighters and RJJ wanted no part of those politics, so they never fought. When RJJ fought Hopkins, it was for the vacant Middleweight title in which the sanctioning body had RJJ the #1 MW in the world & Hopkins as the #2 MW in the world (and BHop was universally recgonized as #2 in the division by the boxing public - thats important later when I talk about Mayweather). Did Hopkins get better as the years went on after that fight? Definitely! But he was still the #2 fighter in the division at that time - you cant knock RJJ for fighting him then. After that fight, RJJ immediately jumped to Super Middlewight and a couple years later, after clearing that division, moved to Light Heavyweight. People saying he ducked BHop for a decade after. They werent even in the same weight class anymore!!! RJJ was reigning LHW champion while BHop ruled the MW then Super MW divisions all of those years. BHop was calling out RJJ, but wanted him to come back down in weight to fight him. Beezy, as a professional fighter, you know more than anyone here about dealing with weight cuts while fighting. Most people claim, myself included, that RJJ was never the same after he moved up to HW for one fight. RJJ even said that getting back down to LHW after that one HW fight completely drained him and was the hardest thing he had to do in the sport (similarly, Antonio Tarver said the same thing about cutting back down to LHW fighting shape after he bulked up to 215-plus lbs for the Rocky movie). So maybe RJJ ducked BHop & maybe he didnt, but I personally cant see how anyone can blame RJJ for choosing not to cut the weight for a rematch against BHop.

So RJJs resume stands as, although fighting his entire career in weak divisions, clearing out everyone in those weak divisions.

Mayweather, on the other hand, cannot make that claim of fighting the best in his divisions. He started off correctly, defeating Jose Luis Costillo twice when JLC was an animal & by easily taking out Diego Corrales, who was destroying everyone at the time. But in the last 5-8 years, Floyd began choosing the highest money fights with least amount of risk instead of fighting the best in his divisions. Example: While Floyd was fighting the overmatched Gatti, Carlos Baldomir (sp?), over the hill Oscar de la Hoya (who even publically states he was finished by that time) - basically all guys that were ranked high in his division, but not considered by ANYONE with boxing sense to be the best in the division, the boxing public and knowledgable fans were screaming out wondering why Floyd wasnt fighting the Miguel Cotto's & Antonio Margarito's of his divisions (basically, the other universally recognized top fighters in his weight class regardless of sanctioning body rankings). Even as recent as a couple years ago, "experts" wanted Floyd to take on Paul Williams, which Floyd wanted nothing to do with. Now hind sight is 20/20 and, looking back, Floyd wouldve almost certainly won every single one of those fights going away. But the fact is we'll never know because he took the money fights against elite names, but obviously overmatched opponents, istead of fighting the best in the divisions (Ricky Hatton & Juan Manual Marquez are two more that fall into that elite name, but overmatched status). Boxing is a career to these guys and I dont blame Mayweather for taking the most money, least risk approach - its smart business by him!!! But I think it tarnishes his legacy a bit. Unlike RJJ, Floyd had guys in his own division that the public considered dangerous threats - Floyd just didnt fight them all when they were considered threats.

So, IMO, RJJ gets the better 4P4 ranking historically for at least fighting everyone in his weak divisions. Although Floyd may actually be more talented in the ring, his choice of cherry picking overmatched money fights instead of fighting the universally recognized best in his division tarnishes his achievements. Although, for the record, I believe Floyd wouldve won each of those fights that I mentioned he avoided and would also defeat Manny Paquioa. We'll just never know because he hasnt given the boxing public the chance to see him against legit opposition in the better part of the last decade.