Daaang, this is going to be a hard choice to make. I really like Dave Foley as Flik and Patton Oswalt as Remy, it feels like they really get into character for their acting. Though I must say, Albert Brooks did such an amazing job with Marlin… he added so much emotion to the sadder scenes in the film.
Does Ben Burtt count? If so, then he’s not only my favorite voice actor from PIXAR but also my favorite sound effects artist ever brought in.
Oh, lord…painful to choose one from each movie…
“You can bring one toy.”
“Just one?” 
Toy Story: Duh!!! Tom Hanks, anyone? Wow…
A Bug’s Life: Dave Foley, hands down. It’s hard to be the obvious choice, when in an all-star cast. Yay Dave!!
Toy Story 2: …hard to choose…Tom Hanks, Tim Allen, and Joan Cusack tied.
Monsters, Inc.: John Goodman. Say what you want for the others, but he made this movie for me. He just brings this lovable warmth with his voice to every role he does. Also love him as Pacha.
Finding Nemo: Albert Brooks, followed not-even-closely by Ellen.
The Incedibles: Definitely Craig T. Nelson. No, not Sarah Vowell. Sue me.
Cars Paul Newman and Larry the CG. No choosing there.
Ratatouille: Lou Romano or Patton Oswalt…or Peter O’Toole. All awesome.
Wall-E: Easily Elissa Knight. *Wall-E? NO!!!"
Up: Ed Asner. No contest.
Toy Story 3: Well, Buzz annoyed me greatly, and Jessie’s character dissolved, so it’s definitely Tom Hanks.
One all-time favorite: Kevin Spacey as Hopper in “A Bug’s Life.” I’d heard of him, but had never seen or heard him in anything before, and was totally won over by him. Hopper has always been one of my favorite Pixar characters, and Spacey just gave him so much charisma.
Favorite Pixar person doing a voice: Brad Bird as Edna Mode. Can’t top that.
Tom Hanks, Peter O’Toole or Paul Newman 
x
Oh my gravy, this is sooooo true. <3
All 3 excellent choices, LovePixar. I like that. You like good actors, not jus okay ones. 
Patton Oswalt is probably my favorite! <3
He is awesome! His voice is so specific, if that makes sense. 
Ohh and I also LOVE Michael Keaton too! Ken and Chick Hicks are two of the best Pixar characters and I don’t think they would be half as amazing without him. He’s just brilliant!
Yeah, I loved him in the first Batman, and was thrilled when I discovered he was in PIXAR movies.
I started to make a list of my favorite performances (not actors), but it was getting to be too long! My absolute top picks are Dug (squeal!), Edna Mode, Heimlich, Woody, Buzz, Randall, Anton Ego, Roz, Russell (so awkward!), and pretty much every Pixar villain. I like the whole original Toy Story cast as well. Uggggh and Mike and Sulley… and I could go on forever.
If I had to pick an actor for their work outside of Pixar, I’d say Tom Hanks, Paul Newman, Kevin Spacey, and Steve Buscemi.
q_o_p: Ah yes Steve Buscemi. He did an excellent job, I agree.
I love Tom Hanks. He’s just in so much good stuff, and several films in my top 20. I’m convinced he’s the best actor of my lifetime. Even if that sounds nuts.
Have you seen Philadelphia Virginia? It’s my favorite non-animated Tom Hanks film! It has two of my favorite actors in it, Hanks and Antonio Banderas. It’s the one where Hanks and Banderas are in a homosexual relationship together, and Hanks plays a character with AIDS and is sues his work for descrimination. Fantastically done. What’s your favorite Hanks movie?
No, I actually haven’t seen that!! I wonder if Starz has it…I’ll check on that.
Either Forrest Gump or Toy Story. A league of their own comes close.
My favorite would have to be Joe Ranft as Heimlich. I don’t think there’s a line he says in the movie that doesn’t crack me up.
Well, even though I say this every day, Tom Hanks is my favorite actor of all time, so he’s my favorite Pixar actor by default.