Cameron by a landslide for me. I only recently (within the last year or two) caught Xenogenesis, his debut short, and the level of talent on display even then was remarkable. When I think of what I want out of a movie - enjoyment, spectacle, heart, cohesive storytelling - he's the one that shows the greatest amount of ability in each category. Not only this, but looking at his filmography (as director alone) reveals not only three of my favorite films (the first two Terminators and Aliens), but also significant works for film as a whole.
Fincher is second but there's a considerable gap. Alien 3 turned out as good as it did through his vision but its faults, though not on Fincher's shoulders, are still there. Se7en, Fight Club, and The Girl with the Dragon Tattoo are my favorites of his, but stuff like Zodiac, Gone Girl, and Social Network either bore or aggravate me. His is a very distinct visual style, too, but that has its benefits and its drawbacks.
#3 is Scott. I have no problem saying he peaked early with Alien and Blade Runner, and even less saying I don't enjoy much of his work at all. Black Hawk Down feels like Ridley trying to do a "mature" take on the technique du jour (quick cuts, drain the color in post, focus on the situation and not characters), Robin Hood is an embarrassment, Gladiator is overrated, White Squall and 1492 are subpar even compared to Lloyd Kaufman's output...but hey, at least Alien and Blade Runner are legitimately great.
Just missing the medals is Jeunet, and that's only because City of Lost Children is amazing.
#5 is the Brothers Strause, with an even wider gap than between Cameron and Fincher. Say what you will about AVPR or Skyline, but at least there feels like a true attempt at doing something somewhat original within genre tropes. Plus? They do some solid VFX work.
#6, worst of the bunch, is clearly Paul WS Anderson. Forget about AVP for a second and remember that his only decent movies were either based on a popular video game with limited lore (Mortal Kombat) or a blend of iconic horror themes of yesteryear (Event Horizon). The RE series is garbage, his Death Race remake was mediocre and bland compared to the outrageous camp of the Corman original, his Three Musketeers is one of the worst takes on the story...just homogeneous crap all around designed to appease the lowest common denominator and make sure his wife keeps a steady paycheck.