I'd definitely vote Boma for the food; just go early and watch the animals before you dine. (Or watch them after dinner; the savannah viewing area doesn't close until well after dark.)
We ate at both restaurants last week, and while it was fun watching the giraffes eat their dinner as we had ours (even though we weren't seated right by the window, we could see out quite well), Sanaa seemed less kid-friendly (if such a thing is possible at Disney...). We were disappointed in the food at Sanaa--we LOVE Indian food, and found Sanaa's a bit bland. (But if you do go to Sanaa, and get the bread service, try the garlic pickle--it was our favorite food of the evening; too bad we got so little of it...)
Boma really does have something for everyone, though it can be a bit hectic. We're vegetarians too, and it's our absolute favorite restaurant at WDW.