We have eaten 3 times at Jiko and each time it has been fabulous - food, service and wine. The first time we visited our server was Ron and he was amazing - very knowledgable about the South African wines and very keen for us to try them. He just kept bringing them! The second time we visited was a week later with my brother and s-i-l and we asked for Ron again. It was within a couple of months of the opening of AKL, so maybe they were making a special effort. We visited again last October. Maybe the server wasn't quite up with Ron, but it's still a magical place for us.
We've visited Boma twice for breakfast and once for dinner. The breakfast is the best buffet we've tried, without question and we've got a PS for the first morning of our next trip (very soon - check my counter!). Dinner, was good too, but I couldn't help thinking about Jiko which is just next door. Boma is a set price. Jiko is expensive - up there with California Grill, Flying Fish, Citricos, et al.
With two such wonderful eateries at one resort, I couldn't even contemplate Mara, although I guess it depends on what you want.
AKL is an incredible resort with a wonderful ambiance, especially at night. Both Boma and Jiko are visually stunning and I don't think you will be disappointed with either. The atmosphere is very different - busy and buzzing at Boma, relaxed and more formal at Jiko, although not intimidatingly so.
Although neither restuarant overlooks a savannah, you must take time to check out the main Arusha savannah and the lobby. Victoria Falls is the lounge bar overlooking Boma. We've spent many a happy hour there! There is also a small bar within Jiko, but it seems to be used as a waiting area and I've never seen anyone serving behind the bar.