I think both are amazing match-ups but for different reasons. Hatton v Mayweather is classic boxer v slugger. The styles clash is exactly that of Leonard v Duran, whereas Cotto v Mosley is going to be a clash of crisp technique, speed vs accuracy and moments of all out war, just like De La Hoya v Mosley, except Cotto is probably has a bigger punch, but not as effective defence. If I'd never seen boxing before then Mosley v Cotto will most likely be a better fight to watch, but personally Hatton v Mayweather excites me more.