Never been to Ohana, but we love Chef Mickey's! We went there for breakfast in July 2008 and for dinner a few weeks ago. Both were great!
The breakfast buffet has a lot of variety, something for everyone. You can eat very healthy there, or really indulge! Character interaction is also great, and you get the see the 5 classic characters.
However, if your family is into Lilo & Stitch, then consider Ohana, as this is the only character meal where they appear, and you still get to see Mickey & Pluto.