If this was in '11, I'd have no problem picking Sergio. However, due to the recent troubles concerning his knee, that ever present question about whether or not his age has finally caught up with him, and the fact that it's in MSG (possible home-cooking or not, Cotto will for sure be motivated for this one), I'm actually leaning towards Cotto. I'd be more solid with my Cotto pick if he brings back that left hook to the body against Sergio.
Segio has the better athleticism and is always somehow able to (for the most part) get away with having his hands low at his waist and his chin stuck out. If he's not careful, Cotto will stick him to death all night with that jab.
Still, no matter who I'm picking for, this is a matchup I have always fantasized about. Can't wait till the 7th, brehs!