Well, my first inclination would be to choose the Goofy's Kitchen character buffet for my one sit-down/table service meal. BUT, it is not quite the standard table service (they do bring beverages to you, but basically you serve yourself) so I am going to leave it out. However, that would be my one choice of a place to eat in all of DLR if I only had one choice!
So, for counter service, I have to say that right now, at this point in time, I am loving Taste Pilots Grill. Excellent BBQ chicken sandwich with great, soft criss cut fries (that look like pickle slices or Ruffles potato chips). They also have great onion rings.
For my one table service/NON-character buffet, that is tough.....I have eaten at Carnation Cafe on every trip to DLR since back in the '90s, and they have good food for any meal of the day, including dessert. But I am kind of burning out on them a little bit. I like Wine Country Trattoria but not enough to choose it over everything else. I like ESPN Zone, Rainforest Cafe and Naples in Downtown Disney, but it seems wrong to choose non-Disney restaurants. So......if I didn't choose Carnation Cafe, then I would probably have to go with Storytellers Cafe in the GCH! I like the cozy ambience there. They have a good lunch menu and they have great spaghetti at dinner!