There is a savanna close to Boma that you can spend some time in before or after your reservation. We ate there earlier this month and after we were done eating, I took my daughter out there to look at animals while my husband finished up and paid the bill.
At Sanaa, we had a table right by a window and an excellent waiter who told us all about the animals and even what some of their names were and how they got those names. It was an excellent experience. If you want to look at animals while you dine, I'd definitely suggest Sanaa over Boma. Then again, if you are just looking for good food, I'd still suggest Sanaa over Boma...