Ive had great meals at all of these in the last year.
Il Mulino at The Swan (Best meal ive had on property in the last 4 years. Blew me away. Get the Grouper, change your life.)
Jiko at Animal Kingdom Lodge(really great resort for arriving early for animal viewing)
Flying Fish at The Boardwalk(awesome night atmosphere as well, easy walk from Epcot if you exit from International gateway)
Monsieur Paul at Epcot(upstairs France restaurant, not the first floor Chefs de France)
Narcoosees at Grand Floridian (If you like feeling ritzy, i recommend Grand Floridian. It can be stuffy feeling, but I find the atmosphere perfect for signature dining)
Citricos at Grand Floridian as well.
You can do well at all of these. Just comes down to checking the menu.
One thing I have found is that you really need to be willing to resort hop if you want to get the best of Signature dining. Outside of Monsieur Paul, I believe the resorts far outclass the parks in signature dining quality.
I left off California Grill cause my meal in November was a solid, "that was fine." I can't in good faith recommend it at this time compared to the above list.