Sadly, I cannot say whether or not these are truly the best, as I haven't eaten in every restaurant in WDW, yet. Those that definitely do not make it on the list include: Chefs de France, L' Originale Alfredo di Roma Ristorante, and the Sci-Fi Dine-In Theatre.
Full-Service...
1. Restaurant Marrakesh (EPCOT, Morrocco)
2. 50's Primetime Cafe (MGM)
3. San Angel Inn (EPCOT, Mexico)
4. Teppanyaki Dining Room (EPCOT, Japan)
5. Crystal Palace (MK)
Counter-Service/Other...
1. Tangierine Cafe (EPCOT, Morrocco)
2. Flame Tree BBQ (AK)
3. Lotus Blossom Cafe (EPCOT, China)
4. Cantina de San Angel (EPCOT, Mexico)
5. Main Street Bake Shop (MK)* and Boulangerie Patisserie (EPCOT, France)*
* - Not really the typical "meal" destinations, but too good to leave entirely off the list...