I have the same dilemma. I think I am going to go with Chef Mickey dinner just because my kids aren't that much into Lilo and Stitch and my daughter would love to see Minnie Mouse. I haven't done Ohana's for breakfast, but I have done Chef Mickey's for dinner before and my kids were quite pleased with the buffet and my daughter is quite the picky eater.
Another vote for Chef Mickey's. Unless you are a Lilo and Stitch fan there is no reason to eat a Ohana breakfast over any other. Many breakfasts in Disney are same-y. Eggs, meat, OJ. The big buffets (CP!) are the ones I wouldn't miss.
Whereas there is a lot of variety in the Chef Mickey dinner menu.
My DH and I did not like Chef Mickey's for dinner. In fact, we refuse to go back. Our children thought it was great though So if it were me, I'd go with Ohana for breakfast. But I'm biased