I always thought Roddick had the best serve, but it wasn't until the U.S open against Fed, that I realized that fast doesn't necessarily equal best. He was struggling to get the majority of his first serves in. I don't get to watch tennis that much, so I don't know if that's a common practice for Roddick but it seems that Fed gets off a lot of aces against his opponents. So I guess I would have to vote for fed. Oh wait, I have to actually vote first.
Well Roddick has a garbage ROS, and Federer has an amazing ROS. So Fed always aces the crap out of Roddick.
Fed also doesn't seem to try to hit hard serve unless he faces a hard server. I noticed this about him. Against lower level opponents he seems to save a lot of energy by not going for big serves.