You will get a lot of differing answers on this. In our experience, most of the food is the same at all of them, with a few exceptions of some items.
Our personal favorite is Crystal Palace for a number of reasons: 1) the puffed french toast, 2) made to order omelets, 3) the characters -- Love Pooh and Tigger, 4) being able to get into the Magic Kingdom early and having Main Street to yourself for great pictures.
We've also done Cape May Cafe and Chef Mickey's. We used to do the one at the Polynesian until they switched it from a "Minnie" breakfast to Stitch (who we can't stand) and they changed it from a buffet to family style.
Cape May Cafe is definitely number two and Chef Mickey's is a distant third in our books.