By seasons I assume you mean working today ... to that I say:
1) Steven Spielberg
The man has been making movies now since the 70s! And while the strength of newer releases ("Indiana Jones & the Kingdom of the Crystal Skull," "The Terminal," "War of the Worlds" among others) remains debatable, the recent "Lincoln" suggests he has a long way to go before retirement. (It's also important to note that other "high profile" directors from the 70s era such as Martin Scorsese and Roman Polanski and even George Lucas have seen their careers practically evaporate. Scorsese in particular, while still a terrific filmmaker, has trouble whenever he steps out of his comfort zone, i.e. crime films. Spielberg has shifted from commercial films to serious subject matter and not missed a beat.)
2) Quentin Tarantino
Every film this man makes is an event film, albeit one that comes with a healthy slew of controversy about its subject matter. For my part, I thought "Resevoir Dogs" and "Pulp Fiction" were both good movies. "Jackie Brown" was okay. It wasn't until "Kill Bill: Volumes I and II" and, to a greater extent, "Inglorious ********" that Tarantino's genius really blew me away. "Django Unchained" was one of the best films of last year - if not THE best. The man knows cinema.
3) David Fincher
"The Girl With the Dragon Tatoo" proved something of a disappointment, but Fincher remains one of the best directors around simply for the unique vision that he brings to every film. In truth, many of the best directors are the best because they don't cater to typical standards. You know when you're watching a Spielberg or Tarantino film. And you **** well know when you're watching something crafted by Fincher.
4) Ben Affleck
Yeah, he's made three movies. But all three have been excellent. I started griping a little after "The Town" when it started to seem like his fixation with Boston-themed thrillers would ultimately be his undoing. Yet, with "Argo," Affleck proved he could tackle something topical, real and informative. I can't wait for his next flick.
5) Christopher Nolan
One of few directors who has yet to make a single mistep in his career, Nolan changed the comic book landscape with his Batman trilogy, then stunned audiences with "Inception." No doubt, everything this man touches becomes an event film. I'm curious to see if his career will expand now that he's hung up his proverbial cape and cowl.
6) Joel and Ethan Coen
The Coen Bros. are hit or miss, and typically require the viwer acertain a particular mood to enjoy their films. That being said, "Fargo" and "No Country for Old Men" are two of the best movies I've ever seen. "True Grit" was more mainstream (at least for them), but I like that they take chances. Their newest film, "Inside Llewyn Davis," doesn't look all that appealing, but you better believe it will be worth the price of admission.
7) David O. Russell
I loved "The Fighter" and "Silver Linings Playbook" (THE best film of last year by a nose), and am eager to see what other crazy human dramadies Russell concocts in the future. (If you haven't, check out "Three Kings," one of the most underrated films of all time.)
8) Alexander Payne
The man gets human drama. Check out "Sideways," and "The Descendants" if you need proof.
9) James Cameron
He deserves to be ranked higher on this list, but since he only comes out with a film once every decade, it's hard to keep him atop the pile. Cameron works his balls off to deliver cinema entertainment. Sure, "Avatar" wasn't the most original property, but even detractors must admit its influence on the film industry. Great directors don't simply make great movies. They change the cinematic landscape. Every one of Cameron's films does just that.
10) Ang Lee
What's so great about Lee is how he continually changes up his style. One second he's making a comic book adaptation like "Hulk," the next second he's making a love story about *** cowboys. Last year's "Life of Pi" blew me away. And while Lee's personal touch isn't readily implicit, there's no denying he's an absolute master of his craft.
OTHERS: Kathryn Bigelow, Woody Allen, Darren Aronofsky.
Another topic of debate would be the most overated directors: Paul Thomas Anderson, Martin Scorsese, and Terrence Malick in particular.