While he isn't my #1 (close!), Paul Thomas Anderson is an absolute genius. His film "Magnolia", in my opinion, is the creme de la creme of all his films. Like a 190 minute long movie that is all about personal human struggle? Any other director just couldn't have done that. You can feel such a personal touch to it. Kevin Smith bashed it hard one time, saying he keeps it at his desk just to remember how terrible a self indulgent movie can be, but I completely disagree entirely. Magnolia was an eye-opener; the scene all about regrets --- that always stays in my mind with the films I make. Am I personally saying something that means anything significant, or just bullshitting to get a reaction? Those thoughts. Magnolia was perfect. His choice of Aimee Mann for the score / soundtrack was incomparable.
My opinion of best director would be Alfred Hitchcock, Martin Scorsesse, or Quentin Tarantino. Can't choose. It would feel like sacrilege.
-Jesse