Here is the absolute final rule about Disney World or Epcot. You have two options for food-
1) Reserve your restaurants well in advance, 10 seconds after you book your flight and hotel
2) Or don't reserve, and you are eating chicken fingers and cheeseburgers in a fast-food style eatery
You MUST, absolutely MUST make reservations if you want to eat at the better places in Disney or Epcot.
In Magic Kingdom, the best places to eat are-
Cinderella's Royal Table (they never talk walk ups)
Be Our Guest (they never talk walk ups)
Rose and Crown Pub (make it for around 7pm so you can sit near the water for fireworks)
Mexico (one of the most beautiful places to eat at Disney)
Japan - Japanese Steakhouse, great food
Germany - All you can eat German food, you'll be stuffed
Canada - awesome steakhouse, skip the poutine, it's not that great
Italy - best place to eat a ton of pasta and pizza
If you plan on visiting, the INSTANT you know when you'll be arriving, get on the reservation line and book your reservations. It is impossible, absolutely impossible to just walk up to a sit-down restaurant and eat. You MIGHT get lucky for lunch, dinner is almost out of the question.