Surf's Up with Mickey at the Paradise Pier (mentioned by DahliaRW above) is the only meal where you can meet Mickey, and usually Stitch too, along with maybe 3 or 4 other characters (sometimes Minnie, sometimes Donald or Daisy, sometimes Goofy or Pluto). This meal is quickly becoming very popular for both character interaction and food. The buffet is not huge, but there are some interesting items in it which are specific to that restaurant (in the past, there used to be flautas and things like that).
Minnie & Friends at the Plaza Inn in Disneyland easily has the largest number of characters - anywhere from 8 - 14 characters, including Pooh, Eeyore & Tigger, Chip & Dale, among many others. Food gets mixed reviews, and the characters apparently come to the tables in rapid succession so you won't be without character interaction for very long.
Goofy's Kitchen at the Disneyland Hotel has been compared to Chef Mickey's. Some WDW vets say they like Goofy's better than Chef Mickey's. Others say they like it less. You will generally see anywhere from 5 - 8 characters, including Chip & Dale, Baloo, a couple of Princesses, Pluto, etc. Goofy's has a breakfast
or dinner character buffet, and the buffet is huge! This is clearly the place with the widest selection of food, and will please even the pickiest eaters. This is a lively environment, and Goofy interacts with the children by dancing or playing little games, pretending to "bake," etc.
Storytellers Cafe Critter Breakfast in the Grand Californian Hotel is laid back, with maybe 4 - 6 characters, including the ever-present Chip and Dale, Koda and Kenai, Terk from "Tarzan," sometimes Meeko, etc. - basically lots of woodsy/jungly Disney characters. You can order off of the menu or from the small buffet.
I think you will get the most character mileage out of Minnie & Friends. You will get the most food and widest food selection at Goofy's Kitchen. And you will likely have some great interaction with Mickey (and surf lessons!) at Surf's Up.