MK:
-We loved the Main Street Bakery-terrific simple sandwiches and fantastic desserts!
-I've also heard rave reviews about Columbia House, Casey's Corner (hot dogs), & Pinnochios, so you might just base it on where you are closest to in the park during lunch.
Epcot:
-If you are eating in Future World, Sunshine Seasons is a wonderful food court in the Land pavilion. Lots of great stuff to choose from.
-If you are eating in WS, your best bet is to snack around the world. There are lots of things to choose from and picking just one can be overwhelming. It;s fun to sample a little from a few places and share with your friends/family.
Animal Kingdom:
-We loved Pizzafari.
-I've also read great reviews for Flame Tree BBQ
DHS:
-We did TS here, so I'm not sure. Lots of CS places have gotten really poor reviews. I have heard good things about Pizza Planet & Starring Rolls, but overall DHS does not have much to choose from. If you get stuck and opt for TS, 50's Prime Time and Sci-Fi would be good choices.
HTH!