I mostly eat QS bc I'm mostly on a budget so here are my favorites from the years I've been going...
Epcot:
Salmon at Sunshine Seasons w strawberry shortcake for dessert
Veggie platter at Tangierine Cafe
Fish & Chips at Yorkshire
Cheese plate (Fromages) from Les Halles w/half baguette
Club sandwich from Kringla (get it heated) w school bread for dessert
MK:
Fish platter from Columbia Harbor House
Corndog nugget meal from Casey's
Beef nachos from Pecos Bills
AK:
Smoked turkey sandwich from Flametree BBQ
Haven't tried Harambe yet in AK but plan to in the near future
HS:
Fried green tomato sandwich from Rosie's but I prefer it without the fresh tomato (doesn't quite mesh well w the fried green tomato, IMO)
Chicken nuggets are always a good bet since WDW has some good ones, not the overly processed ones you get at fast food joints elsewhere
Resorts:
Surf & Surf burger or Mongolian fish from Landscape of Flavors at AoA
Coconut thai meatballs or pulled pork nachos from Capt Cooks at The Poly
African Potjie (stew) from The Mara at AKL
There are many places I haven't tried yet so keep the suggestions coming!