I actually prefer fast zombies, for a couple of reasons.
1: Unless you live in a large city, slow zombies aren't nearly as threatening, as the population isn't as large, therefore the "swarm" effect that makes them terrifying isn't that bad. Whereas fast zombies are always a threat.
2: If a zombie apocalypse ever happens, the zombies will most likely be running, 28 Days Later/Left 4 Dead style zombies. IE: A mutated form of rabies, or some sort of rage virus.
So, I like fast zombies because they're more realistic... That's not really comforting though.
Edit: Though they would slowly decay over time, turning into slow zombies... So that's comforting. Just outlast them!