Is this your 1st visit to WDW? How many days are you staying?
I suggest breakfast at Chef Mickey's - all 5 of the main characters are there (Mickey, Minnie, Goofy, Pluto, & Donald), & it's the only character meal w/ both Mickey & Minnie. Plus, it's located in the Contemporary Resort which just feels very Disney-ish w/ the monorail running through. Breakfast at Chef Mickey's is one of our must-do's!
For your princess meal, I'd do breakfast, lunch, or dinner at Cinderella's Royal Table. Especially if this is your 1st trip! There's just something magical about eating in the castle! We really enjoy eating in the castle - our dinner last year was wonderful! Since you're on the dining plan & may not want to use 2 TS credits or pay OOP, then Akershus (Norway) at EPCOT is nice too - it's in a very "country castle" type building.
If you're spending 2 days in EPCOT, I'd eat lunch at Le Cellier on your Future World day - it's easy to walk to Le Cellier from Future World. And Via Napoli for dinner on your World Showcase day & then stay for Illuminations.
Other character meals we enjoy are breakfast or lunch at Crystal Palace in the Magic Kingdom - it's a buffet w/ Pooh & friends & dinner at the Garden Grill in Future World of EPCOT - it's served family-style w/ Mickey, Pluto, Chip, & Dale & the restaurant slowly rotates through the "Living w/ the Land" ride.
Our kids 2 favorite non-character restaurants are lunch at Sci-Fi Dine In at Disney Studios (you dine in "cars" while watching vintage sci-fi movie clips) & dinner at Whispering Canyon Cafe at the Wilderness Lodge (they love the crazy antics here!).
Our favorite family restaurant is dinner at 'Ohana at the Poly - it's served family-style & is "all you can eat". The banana bread pudding dessert is wonderful! Plus, it's fun w/ hula dancing & coconut races.
We also like dinner at Boma at the Animal Kingdom Lodge (lots of selections on the buffet for both the adventurous eater & the not-so-adventurous eater), dinner at the Kona Cafe (at the Poly), lunch at Liberty Tree Tavern in the Magic Kingdom (the Ooey Gooey Toffee Cake is my favorite WDW dessert!), lunch or dinner at Tony's Town Square in the Magic Kingdom (your server can take your autograph books to the kitchen to get Lady & the Tramp's signatures), & lunch or dinner at Yak & Yeti in Animal Kingdom.
Our kids also enjoyed T-Rex last year in Downtown Disney.
The World Showcase restaurants in EPCOT are wonderful. We try to eat at a different one each trip, but our favorite is Le Cellier.
Our favorite signature restaurant is California Grill - the setting is gorgeous! (But, since we spend a lot of time going back to our kids' favorites, we haven't tried a lot of the signatures...
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Hope this helps some!