MK: I think all the counter service here are fine, except for Pecos Bill (nastiest, driest veggie burger ever).
My absolute favorite though is El Pirata Y El Perico - only open at busier times and usually only for lunch then. It's connected to Pecos Bill though, so if the people I'm with aren't interested in Tacos or Taco Salad, they order from Pecos Bill and I order from El Pirata Y El Perico, and everyone's happy. And just because I dislike Pecos Bill doesn't necessarily mean it's bad, everyone else I've eaten with has thought it was fine.
AK: Pizzafari or Flame Tree
DHS: Pizza Planet (not because the pizza is good or anything, but there really isn't anything for me to eat at the other CS here). I've heard Backlot Express is good though.
Epcot: Sunshine Seasons...biggest variety in one place.