It totally depends on what you like and what your age is. If you are older, (17+) and like elegance, I'd recommend Victoria and Albert's at the Grand Floridian.
If you like character breakfasts, I'd certainly recommend 1900 Park Fare at the Grand Floridian.
If you like quick, casual lunches, I'd recommend either Pizzafari at Animal Kingdom or Cacey's Corner at the Magic Kingdom.
Other places I'd recommend are:
Cinderella's Royal Table (MK)
Citrico's (GF)
50's Prime Time (MGM)
The Grand Floridian Cafe (GF)
I have only eaten at the Polynesian once so I cannot farily recommend a restaurant from there.
There are so many great eating places at WDW, you just have to decide what you like to eat and what atmopshere you enjoy best!