I think Sergio would win a decision. Margarito is an offensive fighter with high activity and Sergio who's just as big as Margarito but very athletic would make him miss with his head movement and would land his very accurate quick straight lefts on Margarito. Antonio would still give some problems to Martinez because he works the body very well, has good stamina and still has a good chin. At the end of the day I just feel like Martinez has too much talent for Margarito at this point in thier careers. He's much better conditioned now than when he faced Margarito the first time, he's also a lot more experienced. He sits on his punches much better now while still being elusive. I would pick Sergio to outbox Margarito in an entertainin fight.
Obviously Margo, as Sergio just proved that he's an overrated hype job, because he had trouble with a talentless hack and they had to fix the fight anyway. But, Margo is shot and was only good because of the hand wraps, so I don't know. Anyway, eveyone's shot and lousy and nobody's beaten anyone of note, because the people they've beaten have only fought shot or lousy fighters. I hope that cleared everything up for you.
I fancy Sergio to win, but it would be alot closer than people think. Would really like to see this fight.