I think I'd have to go Disney... Although I do feel slightly bad about it. Those first nine films are incredibly strong... If we were looking at recently I'd be far happier to go with Pixar, as they are certainly dominant at the mo and I think are doing brilliant stuff.
The two main things stopping me voting Pixar are that I haven't seen them all/remember the ones I have seen and I think there a few weaklings in there. Unlike many I was not a Ratatouille fan and think it is one of their weakest. Also haven't seen Cars or A Bug's Life, and I only have vague memories of the Toy Stories... That said, Finding Nemo is amayzin', and I absolutely adore The Incredibles which I know many others don't (personally, The Incredibles is one of the few movies I've seen with a strong message about nuclear family which doesn't make me want to puke). Also, haven't seen Wall-E yet due to crappy Australian release dates, but I have a suspicion that will almost be enough to change my vote.
At the same time, Disney's line-up is impressive. Snow White, Pinocchio, Dumbo, Bambi, Fantasia, Peter Pan... It's almost unbeatable...