They're both fast in different means. Rafa covers more court through scrambling and is just darn quick. Federer has such good footwork that makes him seem fast.
1. Monfils
2. Blake
3. Nadal
4. Coria (if we can count him...)
5. Federer
6. Gaudio (but I suppose if we can count Gaudio, Coria can be there...)
...
249. Karlovic
250. Junquiera (slow, pot-bellied, yeah...)