Mayweather by UD.
Mayweather would be far too fast on his feet. Floyd would never let Paul control the fight at that type of pace.
If Paul ever fought Mayweather, his punch output would be well under 100 punches a round, probably in the 50-60 range, with probably 5-10 of them actually landing. And this would be due to Floyd being constantly out of range, and then pop-shotting at will.