I think it depends on what you mean by "nice", e.g. who will be going, what type of atmosphere you enjoy, what type of food you like, etc. As Shreggor said above, over time you'll see every place in WDW mentioned as a favorite. You can then find every one of those same restaurants in the "bottom 5" poll.
Those disclaimers aside, here are two groups of my favorites:
Upscale/Less child-friendly (although not child-unfriendly):
Flying Fish
bluezoo
Jiko
Still very good but a bit (or a lot) more relaxed & child-friendly:
Biergarten (our most favorite restaurant of any caliber in WDW)
Ohana
Akershus