It is often difficult to get ADRs even at resort restaurants in the busier times and during Free Dining.
Of those resort restaurants at which I have personally eaten, I can recommend:
Whispering Canyon for the BBQ Skillet;
Kona Cafe where everything was good, especially the sticky wings and fish w/risotto;
Cape May Clambake for the clams and the chowder;
Boma is not my favorite, but it is worth doing for the uniqueness;
'Ohana is yummy and fun;
Hoop De Doo for the whole package;
and Spoodles' breakfast was fantastic.
I have had bad service several times at WDW, but I have gone back to those restaurants and had good service (or vice versa) on subsequent visits. I've never really had *bad* food at any TS restaurant anywhere on WDW property that I can recall, however.
On my next visit, I'm trying several new restaurants. I'll only know if I like them after I try them.