Ahhh, the age-old question. There is no "best" counter service in the World Showcase. There is, however, a worst.

The worst is America. Yes, there is always seating, and it is air conditioned. But it's burgers and chicken nuggets (which, I suppose is safe, and the kids definitely like it). But it's the World Showcase! Go try something else!

We love Tangierene Cafe in Morocco, Fish n' Chips from UK, the bakery in France. We like the Katsura Grill in Japan. I've had a couple of meals from La Cantina de San Angel in Mexico, and it was delicious, but you don't get the amount of food you get in other places. At least, you didn't used to. Admittedly it's been a few years.

I have never tried the Sommerfest QS in Germany. It's basically brats and frankfurters. Though they do have a black forest cake which looks amazing.

However, the best QS place in Epcot IMHO is Sunshine Seasons. If you're at that end of the Showcase, just hop over to The Land and eat.