I would only recommend Ohana for it's breakfast, but not the dinner. Breakfast tend to have better service and served foods properly prepared and cooked. Dinner has proven to be consistently inconsistent in service and food preparation.
The Ohana breakfast is a more relaxed setting and a calmer character interaction, than Chef Mickey's. Its served family style so you are entirely dependent on your server and we found the service to be good back in June 2010. I think many guest do not ask for additional servings, since they have to request it from their server, typically when their at another table.
We also dined at Chef Mickey's in June 2010. Food is still served buffet style, so it has the typical setting tension of leaving your seat at the wrong time..you miss the character(s). Of course, the buffet more or less means you are only dependent on the server for drinks and alerting you of when the characters might reach your table. You will also get a wider range of breakfast offerings than Ohana. Both offer restaurant logo stage prop photos of your party taken before you are seated. Ohana offers the standard lei too.
CM: Mickey, Pluto, Goofy, Minnie, Donald
OH: Mickey, Pluto, Leo, Stitch