Williams by decision, I actually haven't seen enough of Williams to know truly how good he is. But i am seen enough of Margarito to know he is not that skilled but hits very hard and has a good beard and stamina. I expect Williams to take the early rounds, with Margarito coming on around round 4 or 5. The key to the fight is 'sconditioning and chin, if they hold up I think he can outpoint the clumbsy but strong Margarito.
I think Margarito wins by Williams not utilizing his height and reach and eventually Margarito wears Williams down.