MK: Be Our Guest. I haven't had a bad bite there yet. Without a reservation there, I'd do Columbia Harbour House.
Epcot: Tough choice, and it depends on where your plans take you. If you're going through Morocco, we like the Tangierine Cafe. When we're not going around the World Showcase loop, we like both Mexico and Norway. In Mexico, we split tacos. In Norway, there are sandwiches, meatballs, and really good pastries.
Hollywood Studios: Backlot Express, maybe Fairfax Fare... I guess? I mean, the quick service in HS is really just to fill an empty stomach. We haven't found anything super awesome there. However, we have not yet tried Woody's Lunchbox, so we'll definitely hit that for lunch next time and hopefully it will be the one.
Animal Kingdom: Satuli Canteen. Hands down. I am trying so hard to figure out a way to eat here during our next trip, while also getting to try Tiffins. It seems unlikely, but I'm still working on it!