It's hard to have just one favorite:
Epcot - Hype and all, Le Cellier. I've eaten there since it opened and I've always had a good meal.
DHS - I seldom eat there but if I do, I must have 50's Prime Time Pot Roast!
MK - Liberty Tree Tavern but only for lunch, foods decent but it holds many childhood memories!
and best new favorite, quite expensive but worth every penny, the Dolphin's Todd English Blue Zoo.