One day at each park? It'd kill me but I wouldn't do full service in EPCOT. I'd pick a good counter service location instead. ...the Land, Morocco...anything with healthy tasty food.
MK I'd also skip full service. That leaves AK and MGM.
MK=The Castle
Epcot= Alfredo's
MGM= 50's Prime Time
AK= Rainforest Cafe
I really have alot more favorites but I'd never be able to do all of them in a day. It would be very hard to pick just 1 in each park. I just picked the one's we go to most often.
MK-we don't like any MK sit downs.
AK-Rainforest is obvious, but we like Flame Tree, even though it is not a sit-down.
MGM- Definitely Brown Derby!
Epcot- Definitely Teppanyaki Dining room.