I guess it depends on what you like, everyone seems to have a different opinion on these things. I would suggest checking out the menus and then narrow it down according to what you like. We have been to almost every place in Epcot and like things about each of them all for different reasons.
For instance, I would not seek out dining at Chef de France, its not my favorite, but I did enjoy the view from the restaurant and the soup is excellent.
I had a horrible experience at Coral Reef and we would probably not go back again. (It was that bad)

, but I know others that really like it. The view of the tank is a nice bonus at this place though.
Le Cellier is one of our favorites too, as it most others. We consider this place a "must do" every trip, even if its just for lunch.
Anyway, check out the menus and and don't forget about the other little CS and snack options around the WS. You could fill up around the World without any ADRs!
Our favorite TS meals at Epcot are as follows:
(in order of our best of the best)
Le Cellier
Biergarten
Tutto Italia
Tokyo Dining
Our favorite CS options:
Tangerine Cafe - Morroco
Sunshine Seasons
Our favorite Snacks:
Kringla Bakeri - Norway
Boulangerie Patisserie - France
Karamell-Küche - Germany
Yorkshire County Fish Shop - England