I think Oscar and Mosley are among the four lightweights I have who would beat Duran along with Mayweather and WHitaker...and maybe Castillo but probably not. Anyways about comparing Mayweather to RJJ here are the differences... Roy Jones Jr. has alot more power than p4p than Mayweather does, and could hurt Ruiz who was in a weight category 46 pounds above where Roy started at junior middleweight.. Second Jones had better reflexes and speed p4p than Floyd. To compensate Floyd has a way more effective style, and a much more solid defense. I bet if you look at their careers Floyd has been hit less just because Roy would back up onto the ropes, but while Floyd could dominate a fight like he did against Baldomir he never could physically dominate a fight like Roy did pretty much every fight before Glen Johnson ;Tarver I he got control of physically and Tarver couldn't do anything, TarverII Jones Jr. was winning easily until Tarver landed that hook, except Montell Griffin I. Either way I think they both are up there as 1 and 2 in my mind as the best fighters ever, but Roy would have to go first because he dominated everybody with only 1-2 or two close fights in his prime (Montel I, Hopkins)