We have a few favorites:

MK: Columbia Harbour House. A lot of people on here say they love it, but it's still always almost empty whenever we go. I think that's because the menu isn't as mainstream for kids. But we always love eating upstairs on the bridge overlooking the transition from Fantasyland to Liberty Square.

Epcot: Two here...the CS in Japan up in the gardens. No line, good food, and you can eat outside at the top of the gardens. Also the Sunshine Seasons in The Land. It's never empty, but it's amazing that it's not busier. We have been five times, and never tried it until last time. Now it's going to because a must do every time we go.