I think Chef Mickey's is a lot of fun. Its one of only two (I think) meals where Mickey makes an appearance (the other is Garden Grill and I think that's it). Its very lively, they have a buffet at both breakfast and dinner. We almost always also see Minnie, Goofy, Donald Duck and usually Pluto and or Chip/Dale. They have a kids buffet and adult buffet with a pretty wide variety. Its sort of neat to eat at the Contemporary, I know my kids have always enjoyed that. You get to wave your napkin around and clap as Mickey and the other characters sort of cavort around. I think its something everybody needs to do at least once!
I have done both breakfast and dinner, I like dinner mostly because we aren't really morning people!