Here are my family's favorites, starting with the park that we think offers the largest number of good CS options, and ending with the one with the fewest.
Epcot: In addition to the wonderful Sunshine Seasons in The Land Pavilion, we've never had a bad meal in World Showcase. The hands-down CS favorite would be the shawarma platters at Morocco's Tangeriene Cafe.
MK: If we can't count Be Our Guest (which is CS at lunch, but not always available without a FP+), I'd say Columbia Harbor House for me (because I love lobster rolls), Pecos Bill's for my husband and kids (because they're all about the burgers and toppings).
AK: Used to be Tamu Tamu when they had the wonderful BBQ beef and cucumber-mint pita wrap, but apparently once the Disney powers-that-be discovered it was terrific, they took it off the menu to make the mediocre offerings elsewhere look better. We've tried other CS in that park but have yet to develop a favorite, although we often defer to Restaurantaosaurus simply because it's air-conditioned.
HS: We have yet to enjoy any CS meals at HS. Oh, we've had many, but we've never enjoyed one. We avoid eating in this park if at all possible.