Boma and Sanaa are very different. Sanaa is much more of an Indian restaurant with African influences, while Boma is more of a African-flavored standard buffet experience, in my opinion. Both have some middle-of-the-road options, but there is more varied experience at Boma.
That being said, Sanaa is doing more experimenting and envelope pushing than any other Disney restaurant at this point, I think. It is my favorite 1TS restaurant at WDW, and I have sampled many of them.