For theme parks buffets - my favorite is Crystal Palace. I've only been for dinner, but there was a wide variety of food and good character interaction (Pooh characters). Donald is my favorite character, but unfortunately, I did not like Donald's Breakfastosourus. I thought the food there was mediocre and the characters were very rushed. Might have hit it on a bad day because many people seem to love it.
For non-park buffets, my favorite, by far is Boma at AKL. Wide variety of interesting choices.