The best I can do is pick one for each park...
MK - Cosmic Ray's. The food selection is good (I hear their policies have taken a slight turn), you can sit outside right to Cindy's Castle and the main Tomorrowland entrance, Sunny Eclipse plays inside, and they have that great Tomorrowland music piping in from the ceiling.
EP - Sunshine Seaon Food Fair. Epcot doesn't have much in terms of good counter service, but this place has a great selection of food and a lot of room to sit
MGM - Probably Backlot Express. The food is standard fare, but there are many real/fake props scattered around, so it's fun to look at everything. They also play themes to 80s TV shows in the background.
AK - Pizzafari. It's a fun place to eat, the seating area is HUGE, and they have good food too