I stay in the Epcot area most often and my favorite restaurants are those at the Swan/Dolphin hotels. Easy walk and superior food/service. However, you asked for World Showcase restaurants. My top choice is Monsieur Paul. After that I like Biergarten, Marrakesh, and Via Napoli in that order. I think all of the showcase restaurants are at least okay. I cannot comment on Nine Dragons as it's the only one I have not tried.
I also love Tutto Gusto for a quick bite and a glass of wine. Since there are no reservations there, I consider Tutto Gusto to be a hybrid table/counter service choice.
For counter service, Tangierine Cafe is by far my favorite. I also really enjoy stopping into the Rose & Crown Pub for a drink and a Scotch Egg (pub has very limited menu and an even smaller table section!!!) The only counter services I have not enjoyed are the fish & chips stand in UK and the Cantina de San Angel. All of the others are decent. I have tried them all.