MK: Cosmic Rays in Tomorroland for the variety, they're roasted chicken portion is enough to share. A band might even pop up and sing for you!
Epcot: Sunshine Seasons, again for the variety. It is in the Land. It is cafeteria style and you can pick and choose among a lot of different options. Great for when the family can't decide. Also, an overlooked area are the Epcot Hotdog stands which are exellent. If you want burgers I reccomend the Electric Umbrella near Test Track, Mission Space, Ellen's.
AK: We pretty much always eat at Flame Tree. Great food and you can get a nice fruit plate. We've also eaten at the Yak and Yeti CS and it has good food as well but not much variety. If you have a DDE discount, Yak and Yeti wouldn't/couldn't take it (at least not last year - they claimed they lacked the computer capability)
DHS: I agree that DHS is pretty much a bummer when it comes to food of any kind, snacks, CS and TS. For CS I'd reccomend heading toward TOT. There are a bunch of different CS booths (for lack of a better word) and you can choose from burgers, pizza, chicken etc... Great variety.
Some tips:
1. If you want to check out any of the menus you can got to allearsnet and see what they serve. I think the Dis has menus somewhere as well.
2. If you are on a diet or not a big eater, you can always get one double hamburger or cheeseburger meal and then order an extra bun. For just a little extra you get two hamburgers and can split the fries.
3. The fixens bars have tons of things to add to your burgers and Pecos Bills probably has one of the most extensive fixins bars. If you want a "free" salad, ask for an extra carton (thing your food comes in) and plop some lettuce, tomatoes and whatever else you want to put in there. Top it with mayo or some smuggled in dressing packets.
4. You haven't referenced if you have children but AK has no straws. If your kiddos need a straw to drink their soda (or if you want a straw) grab some from somewhere and stash them in your bag before you head to AK.
I think that about covers it. If you change your mind about TS. You can make a ressie from any restaurant, just ask the host.