Hmmm let's see
Mk: Columbia Harbour House. good for variety and it's sort of a tradition for us. Go sit upstairs, it's really cool to sit by the windows and look out at the Haunted Mansion. Also Casey's is a must tradition wise for us. I don't eat hot dogs often, but I always have to stop at Casey's!
Epcot: Sunshine Seasons (?) food court in the Land. GREAT variety and wonderful atmosphere. Good to get fastpasses for Soarin' and grab a snack. The Fish n Chips stand in the UK is a must for us as well. Portion is easily large enough to split (as we have found with most counter service portions, at least for us.)
MGM: I guess I don't really have a favorite here, but I'll say Pizza Planet because it's close to Muppet 3D and I can see it from there (I LOVE the fountain!) Pizza is a slight change from burgers and fries fare at most counter service, it's usually pretty good. I'm not a huge fan of ABC Commissary for some reason, not sure why.
AK: Flame Tree BBQ, certainly. Great portions and wonderful for variety. I love the seating, last time we grabbed a table with a view of Everest! Wait, maybe I'm getting this confused with Tusker House (someone please correct me if I am) but I don't think that I am(?).
Desserts: I can't say it enough, ALOHA ISLE IN ADVENTURELAND FOR THE DOLE WHIP! I read about this legend on the boards, but didn't believe in its powers until I experienced it for myself. We have to go at least 3 times a trip, the whole family are fans! I always get the float with pineapple soft serve, yum!
Also, the sweet cream cheese pretzels that can be found at various kiosks around the parks are a personal favorite of mine. And whatever the cheesecake with the marshmallows on top that they serve at Pop Century's food court. "Cosmic Cheesecake" perhaps?
Sadly, my only bad words are reserved for the crepe stand in World Showcase's France. Maybe it's because I've had an authentic Parisian crepe, but oy...what a waste.
Beverages: I've enjoyed all beverages consumed in World Showcase with one exception-- the Mexican "margarita", it was far too salty for my liking. I had the multi-color-layered one. In the non-alcoholic category, that stand near the teacups in MK, something "grove" I believe, has this wonderful raspberry(?) lemonade slushie type thing. love those.
Ok, I think I've made myself too hungry now, so I will stop.....