Stanley Kubrick, all the way.
On a less objective, far more personal level, I'm a huge fan of Sam Raimi.
And George Lucas is a terrible, terrible director. He's a good producer and business man and he had some good ideas, but he doesn't direct films well. Star Wars was a fluke because he had so many people watching over his shoulders and making sure that he didn't blow all the money.
My vote for best directors are:
Mel Brooks is nothing interesting as a director. If you're a fan of his work; you're a fan of him as a writer. I absolutely adore The Producers, but very little of that is down to the direction. Its strength is the writing and the performances.
And The Producers is probably his best job as a director.
Again, if you like these guys, it's not really because they're great at directing. It's because they write jokes that you like.
Now we're talking. These guys are phenomenal directors.
Another good choice. If only Prometheus had been half as well written as it was directed.
Not a hugely interesting director. Again, I think you like him as a writer and are struggling to tell the difference.
I'm a huge fan of Argento's aesthetic, but I'm yet to see a single film of his that isn't an incoherent mess. I'm not sure that I'd say he's a good director, although he is a very interesting director.
M. Night Shalamyn
M. Night Shyamalan
got 3 great films under his belt, but everything since has been abysmal. I don't know how to feel about him because his first three films were incredibly well crafted, but the later ones are so badly put together that it feels like they were made by a totally different person.
Yet again, these guys aren't particularly good directors. They're funny writers (although they haven't made anything good in years).
Another true great.
Eastwood always surprises me with how good he is at directing.
Richie's best film is Sherlock Holmes, which is a derivative, brainless bit of action fun. His films largely suck, though, I suppose they fall down on their crappy scripts rather than the direction.