Most days, I would go with Roger Federer.

He's been the top-ranked tennis player in the world for 4+ years, after all. 

Tennis?  Let's see: a sport that requires speed, strength, precision, endurance, mobility, strategy....all at once.  Roger's incredible.

This weekend, though, Rafael Nadal did it again.  Won his own 4th straight French Open.  Straight sets.  Over Roger.

Maybe Raf's the world's greatest athlete....