The way you've asked your question - you're likely get a list of favorite restaurants without much explanations.
So let me start here - best food is not necessarily indicative of best theming, and vice-versa.
For instance, in no uncertain terms, I think the food at Sci-Fi Dine-In sucks. And not only do I drive a convertible in real life, there happens to be a drive-in theater in my home town that we enjoy regularly. But I love going to Sci-Fi - because I simply find the theming too impressive. Beauty (theming) is in the eye of the beholder.
Also, in real life, I am a foodie with a pedigree of having lived a storied life enjoying Michelin-starred restaurants in (mostly) New York City, San Francisco, New Orleans, and Europe, as well as, I managed high-end restaurants that would be familiar to just about anyone who has ever visited NYC. Now, just because a person has been to fancy restaurants does not mean they truly know about food. For instance - my friend insisted he was taking me to the BEST Chinese restaurant ever....as he drowned everything he ate in hot mustard and duck sauce - I never took food advice from him again.
Best food at Disney (that is not Victoria & Albert) is served at Swan & Dolphin Signatures - best seafood (BlueZoo), steaks (Shula's), and Italian (Il Mulino). Capa at Four Seasons is also excellent. The Disney-run Signatures serve the best of nothing, but they do offer some great theming; non-Signatures can be fun too. Nothing in Disney Springs, said, "Wow," to us last month...but the ambiance atop Paddlefish made those oysters taste pretty darn good (with a depressing green tomato beneath the crab cake).
Best theming is in the eye of the beholder. CA Grill has no real theming, but it offers an unparalleled view of the Magic Kingdom. And despite the fact that we stay at Contemporary (Bay Lake Tower next door, really) with a view of the Magic Kingdom from our room, we eat here every vacation. However, other than maybe recommending their brunch, the place is too hit-or-miss when it comes to their food for me to make a recommendation because of their food. In other words, I would not go out of my way for CA Grill because of their food, but if you could only dine at one place without going into a Park, this is the place I'd be recommending - because of the view.
Sanaa is likely my favorite themed place - because the food is pretty good AND you can enjoy the animals on the Savannah (during a daylight meal)....and it's inside the most impressively themed resort.
Coral Reef is very cool - because the room is amazing....but there are people on the Dis'Board whom I do respect for their food knowledge - folks who find the food at Coral Reef to be the polar-opposite of my favorable experiences.
50's Prime Time is very cool too - but only if you ever experienced black & white TV's (with knobs), formica tables, etc. The theming is lost on most children.
Similarly, Brown Derby is from an era in Hollywood that no longer exists...with the most popular dish being a salad.
Cinderella's Castle is visually amazing, but I insist the food only tastes amazing after Jasmine visits our table.
For the price of admission - Hoop Dee Doo Revue is an amazingly fun time...but they serve cold food (that is kinda' intended to be served hot) - and yet, worth the price of admission (if you can find the place).
It rains inside the Rainforest Cafe.
You can feel the claps of thunder if dining in the West Wing of Beast Castle (and meet The Beast only at dinner) - another of my favorites.
You may be an American history buff, so Liberty Tree Tavern costumes could make you smile.
My child has sorta' outgrown character meals, but I melt every time I hug Goofy at Cape May or Tusker House - so it's not about the food here either.
Everyone who is going to offer you advice has their favorites....and there would be others who will suggest that these same places were the place(s) where they had their worst experiences.
