Walt Disney World has a ton of great places to eat--there are multiple restaurants in each park, hotel, and Downtown Disney--so it's difficult to focus on just ONE that's the best. I've eaten in several of the restaurants, however, so I can try to provide some help based on personal experience!

Magic Kingdom:
1. Cinderella's Royal Table: You actually eat INSIDE Cinderella's Castle, which is obviously way cool. The restaurant itself is upstairs with views of the rest of the park. The menu is prix fixe with a choice of different entrees. Standard American cuisine (pastas, sandwiches, salads, chicken or fish entrees, etc), but good.
2. Crystal Palace: Character dining with Winnie the Pooh & friends (different characters come up to your table during your meal for photo and autograph ops). Buffett-style with lots of different choices.
3. Tony's Town Square: Just your standard Italian restaurant, but with a "Lady and the Tramp" theme.

Epcot:
1. Akershus Royal Banquet Hall: Character dining with the Disney Princesses. Norwegian food.
2. Biergarten: Buffett with traditional German food and beer. A live band performs during your meal, and you're seated at long tables making you feel like you're at Oktoberfest.
3. Le Cellier Steakhouse: Canadian themed steakhouse. The cheddar cheese soup is famous and delicious. Pricey.

Hollywood Studios:
1. The Hollywood Brown Derby: American cuisine, a bit upscale. Based on the original Brown Derby restaurant in Hollywood that invented the Cobb Salad, so make sure to try Disneyworld's version--it's delicious and HUGE--serves 2-3 people easily.
2. 50's Primetime Cafe: Classic comfort foods, served in what feels like a 50's kitchen. Black & white TVs play classic shows.

Animal Kingdom:
1. Tusker House Restaurant: Exotic dishes for lunch & dinner, but they have a character breakfast buffet that features Donald, Daisy, Mickey and Goofy in safari gear.

Downtown Disney:
1. House of Blues: Southern classics, this venue also hosts many concerts.
2. Raglan Road: Irish pub with delicious Irish-themed food, as well as Irish dancers and musicians that perform daily.

There are many, MANY more restaurants in the resort, but these are just the ones I can personally vouch for. There's quite a range in prices, too, so be sure to check out Disneyworld's dining website to see which ones fit your budget. Happy dining!

**Note: For many of these restaurants, it's a good idea to make a reservation (in fact, I'm pretty sure some of the restaurants REQUIRE one). You can do this by calling (407) WDW-DINE (or (407) 939-3463).

I found some great listings on this subject, ranging from recent to a few years old. So feel free to pick and choose.

http://www0.epinions.com/review/trvl-attract-Walt_Disney_World-Dining_and_Entertainment-Dining/content_180555583108
http://themeparks.about.com/cs/disneyparks/a/WDWbestDining.htm
http://orlando.about.com/od/disney/ss/disneydining.htm

The best place I remember eating at in Walk Disney Worlds was a buffet where some of the characters walked around. I think it might have been Chef Mickey's breakfast buffet. They had Mickey, Minnie, Chip, and Dale inside the restaurant. They also served the amazing Mickey Mouse Waffles.