Interesting question. I would say Marquez because of the Pacquiao knock out. Mayweather's last legitimate KO was against Hatton. Besides him and Corrales, Mayweather has never knock out a significant opponent, however.
Pacquiao has been hit by big guys like Clottey, Cotto, Margarito and none of them could drop him. Although, this last fight could be that Pacquiao was just worn down after being hit through so many fights but I'm giving Marquez the benefit of the doubt because Pac looked great against Bradley only a few months ago.