MK - Not a big fan of most of the quick service places. The waffles at Sleepy Hollow are always a must get (I believe they are just available for breakfast right now, but that might change before you go). The citrus swirls at Sunshine Tree Terrace are really good, especially if your not very big on dole whip. Pinocchio Village Haus is fine, but certainly not great. It can be fun to watch its a small world while you are eating though! I also must say that Cheshire Cat Tails are really yummy treats (you usually can get them at Cheshire Cafe, but I believe they’re currently available at Cosmic Rays), and Gastons Tavern has really good croissants, cinnamon rolls, and of course the Lefou’s Brew!
HS - We don’t typically do QS here, as we usually go to Sci-Fi, but Docking Bay 7 has some good options. Snack wise, Woody’s lunch box has really good pop tart like pastries?? It sounds kind of strange, but they’re actually pretty good! The Jack Jack num num cookies are also very good, and I really love the ice cream at Hollywood Scoops.
AK - I actually think AK has some pretty good QS. Restaurantosaurus has burgers, hot dogs, chicken, and stuff like that. I’ve had the burgers in the past and they were pretty good. Satu’li Canteen in Pandora is AMAZING, one of my favorite QS restaurants in WDW. Pizzafari also has some good QS, we’ve gotten the pizza there plenty of times and it’s great. As for snacks in AK, the Night Blossom at Pongu Pongu is really good (this is a drink, but definitely worth it, there are also alcoholic versions for the adults), and Dino-Bite Snacks has really great Strawberry Shortcake ice Cream sandwiches.
Epcot - Sunshine Seasons is probably you best bet for QS in Future World... or whatever they call it now. The best way to describe SS is like a giant cafeteria, the food isn’t great in my opinion, so I would try to save your hunger to eat in World Showcase! I’d heard the BBQ is really good at Regal Eagle, but I’ve never been so I can’t confirm, if your into BBQ though, maybe give it a try! Lotus Blossom Cafe in the China pavilion is so underrated, and has great Chinese food. The Mongolian Beef Combo is amazing, and I would definitely recommend! La Cantina de San Angel in the Mexico Pavilion has delicious Mexican food, and there are plenty of options. The Patisserie in the France pavilion has great pastries, and L’Artisan des Glaces (also in France Pavilion) has incredible ice cream. Kringle Bakeri in the Norway Pavilion also has really great pastries, so maybe try it as well! Kabuki Cafe in the Japan Pavilion has INCREDIBLE Japanese shaved ice. There are so many different flavors to choose from, and it is so delicious. I’ll also add that the funnel cake in the American Pavilion is really good. You really can’t go wrong with anything in World Showcase (and I would say, especially if you won’t be going for awhile after this, splurge a little and do one table service in Epcot, it’s worth it if you can!)