There is so much variety, that you might want to define your question a little bit more specifically. The answer will probably vary depending upon whether you are interested in a character meal, a meal in the parks, ethnic food, etc.
From an overall quality of food/atmosphere/service perspective, we really like the California Grill, at the top of the Contemporary Resort. As a bonus, if you're lucky and you time your priority seating request right, you might be able to watch the MK fireworks show "Wishes" from your table with the music to accompany the fireworks piped into the restaurant.