I think Margarito has almost the perfect style to beat Tszyu. Very aggressive and strong, won't allow Kostya to get a lot of extension on his power punches, and has the chin to take the incoming. As long as Antonio didn't take too many flush right hands, i think he breaks Tszyu down and stops him late.
Call me crazy, but P4P I actually think its a pick em. If we're talking about the prime 99-00 Tszyu. Margarito's pressure would be a big prob for Tszyu, but Tszyu's power, speed, and accuracy would be hell for the defensively challenged Margarita as well. With a gun to my head, I'd probably pick Phony, but Tszyu wouldnt be w/o a chance. In an actual matchup at 147 though, its no contest. Margarito would beat Tszyu half to death.