Not necessarily the best, but who's your favorite all-time writer and artist (or writer/artist). Sub-question: what's your favorite work they've done?(feel free to contribute your answers in the comments)
Ben
Matt Wagner hands down. He alone is responsible for me staying in comics. In the late '90s I wasn't reading either of the Big Two and was only picking up a handful of indies. Then
Mage: Hero Defined came out and the whole series blew me away. I went back and picked up the first series and it was sort of everything I needed: magic based in reality, angst, a glowing baseball bat. For a while it was the only book I collected. While there have been a great number writers and artists that I respect and whose work I love, Matt Wagner will always be my answer to this question.
Big Mike
Favorite writer... I guess it has to be Grant Morrison. His run on
New X-Men is why I started reading comics again... but I would be lying if I said I didn't have a hardcore soft spot for Denny O'Neil... yes, I realize that's not a very cool thing to say.
Favorite artist is Mike Mignola. He's a guy that draws for the story. If more artists drew for the story instead of trying to make sure we can see the outline of Batman's asscrack, super-hero comics would be a hell of a lot more readable.
DevonAll time favorite writer?
Mind you, this is more out of gratitude than anything.

Larry Hama, the man was a true universe builder. Never mind the fact that he pretty much single-handedly created the G.I. Joe mythology but once a year, due to the rollout of new figures and toys, he had to introduce new characters and storylines while wrapping up existing ones.
He wasn't the greatest storyteller but the man was a giant when it came to world-creating.
As far as my favorite work of his? Has to be
G.I. Joe #34, "Shakedown." I learned what honor amongst men truly meant in that
issue.
As far as my fave FAVORITE writer goes? Grant Morrison because even when he misses he does it spectacularly.
My favorite Morrison?
JLA #6 & 7. The JLA vs. an invasion from heaven. It's just so "Grant!" Superman moves the moon using his newfound powers while the current Flash and former Teen Titan, Wally West acts as us, the reader, channeling the astonishment of seeing the heroes he grew up with going all-out. Great comics!
GraigWriter: Keith Giffen - The most resonant comic book experience I've ever had was with the "Giffen-era" Justice League. While it was far from a solo effort on Giffen's part, with some spectacular artistic talents in Maguire, Templeton, Hughes and Sears, and two incredibly talented (and funny) writers in J.M. DeMatteis and Gerard Jones, the common link was Giffen. That era of the JL presented something that every team book strives for, but rarely ever achieves: family. Just as deconstructive of the superhero genre as Watchmen, just differently so - we see the team in their off-time, all their interpersonal quibbles, and the way their battles with "the bad guys" (in various shades of gray) affect them, and not just the fighting. That other Giffen-influenced series from
Annihilation to
Common Foe to
Hero Squared have all have been to some degree or another damn awesome, I'm almost always ready to follow Giffen to whatever title he finds himself plugging away on. Few other writers have been able to so consistently entertain me with their ideas and their execution thereof.

Artist: Mike Parobeck - I don't know of another single artist who could produce such simplistic-looking artwork, so precisely and so effortlessly. Dozens upon dozens of other artists have come along working their hand at the "Animated" style of comic-booking, attempting to emulate the design work of Paul Dini and Bruce Timm's Batman/Superman cartoon series, but it was Parobeck who nailed it, did so not in their style, but his own. If you look at his work on the Impact series "The Fly" or "El Diablo", you can see the work of an artist who had complete control over every single image he drew, and in its simplicity was utter beauty. Parobeck died from diabetes related complications in 1996 at the age of 31. Like other phenomenal talents Seth Fisher and Mike Weiringo, he left us far too soon, before he created his masterwork, but then everything he laid pencil to is worth a read. While his
Batman: The Animated Series will no doubt stand highest as his greatest contribution, his vibrant but short-lived
Justice Society of America is my favourite.