We've went to Chef Mickey's at least 4 or 5 times and O'hana 3 times. With kids 5 and 7, I'd vote for O'hana. They have a parade where music from the Little Mermaid Plays "Under the Sea" and all the kids parade around the room with the characters. The food is good, Mickey waffles, sausage, bacon, scrambled eggs and some sort of pineapple bread and it's brought to your table, but you can have as much as you want. Characters are dressed polynesian style. Mickey, Goofy, Pluto, Chip and Dale were there and come around to your table.
At Chef Mickey's, it's buffet style, which is also good. Every 15 to 20 minutes, the characters do a little dance and everyone swings their napkins in time. Mickey, Minnie, Pluto, Chip and Dale come around and Goofy usually stands by the buffet.
Either place is good, it just depends on whether you want the kids to get up for their food or to get up to parade with the characters.
We've been to both and the kids under 10 seem to have more fun at O'hana's. We went in October, 2003 to O'hana's and it was very slow so the characters spent a lot of time at each table - my son is 15, so he was not as impressed as I was!
At both places, characters come around to your table.