If we're talking restaurants that aren't the most liked, I'd probably go with Coral Reef. We've had lunch or dinner there at least a half-dozen times, and we've never had any complaints about the food. The other diners, well, that's a different story, but a two-top right in front of the aquarium is one of the best seats anywhere in Epcot. And here's some crazy truth for you: on our honeymoon last year, I had octopus at Coral Reef and at Victoria & Albert's. It was better at Coral Reef. V & A overcooked it to the point where it was kind of rubbery and a little bland, and Coral Reef's was tender and delicious, almost scallop-like. Was it a fluke? No, it was an octopus, but it's still a true fact.
Now, if we're talking popularity based on the amount of discussion that surrounds them, my answer would be Il Mulino. Sometimes I feel like I'm the only one who talks about that place on these boards. It is by far the best Italian food to be had inside the Disney World bubble. Not a single other Italian restaurant comes close. It's a signature experience, to be sure, but the value is fantastic when compared to the alternatives. I hesitate to say that I think more people need to discover this place because I love being able to get a walk-up seat in the bright, clean lounge or the warm, comfortable dining room at pretty much any time of any day.