WCC was the first one to pop into my head. At breakfast, they have a pretty good platter that's all you can eat. Not the best use of a dining credit, but great for oop. For dining credits I'd probably choose later in the day. For lunch or late breakfast break from MK, it's kind of a nice break. At dinner it probably gets crowded again (haven't been for dinner), and I think the early morning there is probably also more hectic.
Another thought - is the forgotten character meal at the Swan. It get's reasonably crowded at dinner, but less so at breakfast. Goofy actually spends time interacting with guests rahter than running from table to table ina hurry like at other character meals. Even the dinner is good in that way.
Another fun one - in a way - that nobody knows about is the QS at GF. It's relatively uncrowded, esp in the middle of the day and dinner. You can take your food outside and watch the MK/monorail from a distance. Not the same constructed 'fun' as 50's PT or WCC to be certain, but special nonetheless. It's so quiet and peaceful - and a great view of the castle. It's a nice spot for reflection. Plus, it's on the water. The food isn't bad either.