I voted for John Carpenter, but I wanted to vote for Tobe Hooper and Clive Barker as well. One of the best directed horror movies was done by Stanley Kubrick: The Shining. I'd rank that up there with Texas Chainsaw Massacre and Night of the Living Dead as being three of the best directed horror flicks.
Wes Craven's had a fantastic horror career and made some really outstanding movies in his life. I think recently, however, he's gotten a little full of himself. He's hoping low-quality work will run just because he's associated with it. He's also started putting his name on some bad, bad stuff that he has very little hand in- (case in point- "They"😉 ...I guess it's possible his career is just winding down, but I'd bet he's still capable of putting out something special... still, I'm not really holding my breath.
I love Alfred Hitchcock, but there's something about him-- like he's the default horror director, or something. It's like being a fan of Shakespeare, you know? Of course, that's certainly not his fault, and it doesn't diminish his skill as a director.
Clive Barker, I've always thought of more for his writing than his directing. *Shrugs* John Carpenter's okay, but he's defiantly not my favorite of the people here. George Romero, Tobe Hooper and Dario Argento are AWESOME, uh... Damn, can I just pick all of them?
Also, why isn't Ed Wood up there? ^_^ (Notice: I say favorite, not best)