Based on quality wins, Mayweather gets the nod. Mosley beat no one besides Holiday at 135 , that is why he was able to dominate and have all those Ko's.
Mosley may be more physically gifted, but Mayweather is the more skilled and smart boxer.
Mosley's not going to outbox Mayweather, and his "power-boxing" (speedy slugging) style is not the type of in-your-face aggression that bothered Mayweather against Castillo. Mosley winged a lot of shots and left himself open down the middle, which Mayweather would most likely capitalize by landing straight rights and maybe short left hooks as well.
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