There are so many to choose from and I hear a new one is going in Hollywood Studios, which I think is a really good idea, but if I had to choose one from each park I think I would go with.....
Magic KIngdom - Pecos Bill's
EPCOT - Tangierine Cafe, although I've never actually eaten there (but I have eaten at Marrakesh) the fare there sounded good. We've eaten in Sunshine Seasons which has a wide variety, food is ok. I wish Italy would have a CS.
MGM/Hollywood Studios - Not a big fan of MGM/HS food, so like I said above, I'm glad to hear more is going in there. But I guess I go with Rosie the Riveter Cafe
Animal Kingdom - Flame Tree Barbecue
Downtown Disney - The Earl of Sandwich