Depends on what you're going for.
If you like the classic characters, and want really excellent food, go to Chef Mickey's. They have one of the best buffets onsite that I've been to. The character interaction is pretty good - the service wasn't great (no one seemed happy to be there, when we went) but the rest of the experience was good and the food made it all worthwhile. Not super upscale brunch type food, but good/different/interesting as well as the standard breakfast fare.
If you don't like the germ-factor of a buffet, or have kids that you need to get and carry food for, I'd go for Ohana. The bread they bring out includes a pineapple bread that is to die for. The huge skillets of eggs/bacon/sausage are okay - nothing to write home about, but good enough. The fruit was wonderful (we got three plates of it), the aforementioned pineapple bread, and the Mickey Waffles were a big hit with the kids, as always. BUT - the servers are SO friendly and interactive here (Maybe because they come to your table so many times during the meal) and always happy to bring more (without us having to ask - they would offer first). The character interaction was awesome - Lilo and Stitch were really funny and spent lots of time at each table. They (without being asked) posed and interacted with each of our kids, held hands with them during the musical parade around the restaurant, even "told" them stories and were so gentle and sweet when the baby was scared at first. They also interacted very nicely with an adult couple seated near us, celebrating their anniversary. All in all, this was a vastly more pleasurable character breakfast for us (even if the food wasn't memorable - and that says a lot for a couple of foodies).