You'll laugh at this, but the one my family always hits, even if we are staying elsewhere, is the Roaring Forks at Wilderness Lodge.
It's just a fast food place and just an average one. But my youngest son has a very strong attachment to the place. (Perhaps because we were in the Wilderness Lodge the first time I let him have charging privileges with his room key, so he could eat all the chicken and fries he wanted.)
In any event, we never miss that one for at least one meal during the trip.
But seriously, others at top of list include Columbia Harbor House and Cosmic Ray's in the Magic Kingdom, Sunshine Food Fair at Epcot, Sci-Fi Drive Inn at MGM and Flame Tree BBQ at AK.
As to real meals, I'm partial to Artist Point at Wilderness Lodge