Wow...
I *like* a lot of characters, but favorite characters EVER?
Veronica Mars
Cute is nice, cute and smart is nicer, cute and smart and tortured and pathologically lying and making a living out of it? Being right and still being wrong all at once? One of the best female characters ever to set foot on the airwaves.
Dr. Gregory House
I don't think many can compete one-liner for one-liner with House. He's a factory for the things, and he's pretty danged smart, as well as the whole torture-factor. What's more, he is a character that actually grows. Grows! He's one of the most fun to analyze characters I've ever seen, and he doesn't just hold a show together, he IS the show, and it takes a big character to do that with an ensemble cast.
Hiro Nakamura
We can say a lot about how heroes went wrong, but one thing we all know it got right in the first season: Hiro Nakamura. Infections, honorable, heroic, immersed deep in the mythology. He functions as a heroic comic relief in an ensemble cast. That's new, and I'm incredibly proud of the way it was done. I still have his Takezo Kensei sword on my mantle today.
Malcolm Reynolds
Rarely does a character embody the kind of leader you would implicitly follow. It's often shot-for, often assumed, but rarely is it earned on camera. There's no question why Malcolm Reynolds is in charge of Serentiy. Between straight talk and hard decisions, he's a man among men, but not so overly that he can't be quirky, and downright comical at times. All of the characters on this show are exceptional, but Malcolm somehow outshines them all, and not just because it's 'his show.'
Batman
I don't think there's anything more defining in the 90s and early 2000s for Batman than Kevin Conroy's voice and the muted grays which defined the Animated Series and spawned a whole separate DC Universe, with its own continuity, demands and fans. It was a distilled version of the character that is still identified with as a 'classic' or 'typical' Batman, as opposed to the not-quite-yet-there-mentally Ninja Baleman or the not-quite-alive-or-dead-either omniscient psychopath the comics are publishing.
These five to me, are master characters. They cannot be substantially improved. It doesn't hurt that they're surrounded by other great characters.
Assorted Others by Show:
Arrested Development -> Maebe Bluth, "marry me"
The Office -> Stanley, best deadpan ever!
Stargate Universe -> Ronald Greer, hardash played with a heart of gold, love it!
Lost -> Ana Lucia, I loved the way she was positioned in the story, I wish they knew where it was going earlier so she could have found a permanent home.
Boondocks -> Huey Freeman, I know we're supposed to like him, but he's even better than he needs to be.
Studio 60 on the Sunset Strip -> Matt Albie, hated the actor until then... a great 1st arc