For breakfast, our favorite place is Kona Cafe at the Polynesian. Try the Tonga Toast or Pineapple Macadamia Nut Pancakes. Great coffee, too! Waits can be long, so make an ADR if you know what day you'll want to dine there.
For buffets, my family enjoys lunch at Biergarten in Germany (Epcot) and dinner at Boma at Animal Kingdom Lodge. We also liked the dinner buffet at Trail's End at Fort Wilderness.