Mayweather. Mayweather has very underrated power and a very good defense. And at 140 when I saw him against Gatti he seemed to have a lot of pop on his punches and hit very hard. But Mayweather at 140 is very fast, the fastest opponent Pacquiao has faced, maybe not as fast but then again Marquez wasn't as fast as Pacquiao and was still able to time him and counter him. Mayweather has a better defense and is arguably a better counter puncher then Marquez and I think he could give Pacquiao a lot of fits. He won't stand in front of Pacquiao and trade he will box him.

Mayweather also has a very good chin and has never been down. Which is even more trouble for Pacquiao if he catches him.

Floyd Mayweather UD if the fight takes place. Would be a good fight. But a lot of people would hammer Floyd for not "standing and fighting" with Pacquiao.