Wow, that is such a hard question because so many of the restaurants at WDW are wonderful. If I had to choose just one, I guess I'd pick
Artist Point in the Wilderness Lodge resort. This is one of Disney's signature restaurants that has a bit more of an upscale feel to it. I find the craftsman style interior to be exactly the right blend of relaxing and elegant. I've dined there 6 or 7 times and have always been impressed with the food and service. Plus, they have a lovely wine list.
If I had to pick my favorite restaurant in a theme park, it would be either the Brown Derby in Disney's Hollywood Studios or Teppan Edo in the Japan pavilion at Epcot.
And my favorite restaurant for big groups is the Whispering Canyon Cafe, which is also in the Wilderness Lodge resort. The big skillets of ribs and chicken are YUMMY and there is always enough entertainment from the servers to have children of all ages leaving with big smiles on their faces.
Gosh, I'm hungry just thinking about all that great food!