As you can see from all of the above, there are endless good choices and it is really down to personal taste. I would have a look through the menus on Allears.com and this site and see which float your boat.
As far as Epcot goes, I think every World Showcase country has a decent QS, depending what type of food you prefer. Some excellent choices are also available at Sunshine Seasons but the surroundings are canteeny, especially compared to some of the places around the lake. The only poor meal we have had at Epcot was Electric Umbrella.
MK, I haven't yet tried BOG but their QS lunch is getting raave reviews, the only downside being massive lines to get in from early morning onwards. Columbia Harbour House and Sleepy Hollow are good and Cosmic Rays has plenty of choice and some outdoor tables overlooking the castle.
AK doesn't have so many, but Flametree BBQ has come decent enough food and the setting is to die for, lots of samll terraces overlooking the lake and views of Everest. Anandapur Local Cafe is also good although it can be hot and busy there, and TamuTamu had some good sandwiches last year, which we carried over to the Dawa Bar to eat with our cocktails!
As for HS...... well, Starring Rolls has nice sandwiches and cakes............ Actually we were caught in a thunderstorm last year and just for shelter we called at Backlot Express. I had a turkey sandwich and it was surprisingly good (and the beer was even better)
Downtown Disney must-dos for us are Wolfgang Puck Express and Earl of Sandwich, and we are considering Cookes of Dublin this year due to Rave reviews from a certain quarter on here.
Good luck with your choices, and have a brilliant holiday.