Mayweather is an awfully skilled boxer, but not a pressure fighter; not at 140+lbs anyway. If Mayweather hasn't lost much of his form of two years ago, i'd still favor Floyd, but it would be one hell of a fight and probably a close one.
Cotto has nothing down the stretch, Mayweather sahres the early rounds with him and turns up the pace and ko's Cotto down the stretch
Mayweather's condition would be a big factor. Let's see what he has left in the tank for the JMM fight. But if I had to pick right now based off where PBF left off last Vs. last night's Cotto. I'd pick Floyd to win a rather easy UD/or possible stoppage late.