Mayweather is so boring to watch. It seems like all he does is get a few jabs/counter punches in, then dance away. He can dominate a fight by unanimous decision, but most times he doesn't go for the KO, apparently because he isn't a power puncher by trade.
That said, I would like to see Pacquiao fight someone who is quicker and can put up a better defense. Hatton was dominated because he's quite slow (that showed in his fight vs. Mayweather too), De La Hoya was well into his decline, and as for Margarito, yes, he's 30 pounds heavier and has a better reach, but he's also not fleet of foot. Clottey was too defensive of a fighter to give Pacquiao a serious fight. Speed for speed, it seems like Pacman and Mayweather are a match, but Pacman is lightning quick with his punches and hits hard.