Slow zombies. Fast zombies, co-ordinated zombies, and clever zombies are not zombies, they are some other creature entirely. Also, they lose most of their horror - why? Because the whole point of zombies is that they are so easily outwitted, and so easily outrun, and if you've got anything remotely resembling a decent weapon they're easily killed, but they
will still get you. It's the crushing inevitablity of their numbers, their lack of fatigue, and the complete perfection of willpower which makes them scary.
Fast zombies give no time for the involved character to have any interaction with them. There's no horror or fear, there's just "OHCRAPAZOMBIE*Blamblamblam*OKITSDEADNOWK!".
I can't remember where it is, but Simon Pegg (Shaun of the Dead) wrote a vey good little piece along pretty much those lines.
So yeah, slow, ambling, mal-coordinated zombies. If they have to exist at all.
