I would pick Margarito to win by TKO.
His pressure and workrate would be too much for the Smaller Berto.
There is a chance that Margarito has become shot after his one sided beatdown against Mosley.
I think Berto is too fast for Margarito(no plaster) and decisions him. He'd use lateral movt, pepper Marg, and get out when Marg starts firing back. He's fast enough to do it.
I don't think Berto has the power to hurt Margarito, even if Margarito's chin isn't as good as it used to be, Berto's speed and movement could give him some trouble early but once he gets going, he'll wear Berto down. Margarito by knockout.
This is why I think Berot should take a gamble and fight margarito when he comes back. For one we don't know if Margarito's power is artificial. If it is Berto can win, if it isn't he gets knocked out.
If Margarito's punching power is in fact a natural attribute, then he could stop Berto late. But we don't know if the fights with Cotto & Shane have ruined him.
If its the Berto that fought tonight, I say Margarito is too big and more importantly too active for him.... Berto needs to learn to handle pressure better.
Despite everything I think Margarito still displayed a solid chin in addition to his size; I think Berto would have problems backing Antonio up. Even if his power is less than it was, Margarito will be larger than Berto and, I think, be busy enough to win this fight. Possibly catching Berto late and stopping him even.