We had dinner at Boma and enjoyed it very much. It is an extensive buffet with numerous African themed dishes but plenty of traditional fare if you don't go for the exiotic. There is also a kid section to the buffet with regular food for the kids.
The food court "Mara" has plenty of quick meals, salads, burgers, pizza, etc. Also a small shopping area with snacks, drinks, etc. Had breakfast there and it was fine.
Did not try Jiko but the menu looked very good, a little on the pricey side.
Get a PS for Boma or Jiko.