If I had to choose I'd probably do Tusker House breakfast and Boma for dinner. I really liked Boma for breakfast, but the only thing that really stands out in my mind a few months later is the goat cheese scrambled eggs, while a few years later, I still remember several things from Tusker House, the sweet potatoes, bread pudding, and some kind of egg and meat casserole. I also found the service to be better at Tusker House, and the location, unless you are staying at AK Lodge is much more convienant.
Boma for dinner is wonderful. I love the soups, varieties of hummus, and most of the meat dishes. Plus the desserts are really good.