I was trying to get to Botswana a few years ago, but never made it. I've been wary of Kenya for a few years, both for political reasons and because of how touristy I've heard it has become.
I was in the Serengeti (Tanzania) in March, Masai Mara (Kenya) in April, without a doubt the Migration was better viewed on the Serengeti side, quieter, less hectic, less People.
The actual Mara River Crossing is probably better from the Kenyan Side (More Options), but you then have to contend with a lot more vehicles competing for the same spots, it can sometimes spoil the experience.
Now, with the latest ongoing drama in Nairobi, we have Terrorism to contend with, in future I'll work on fly in/fly out same day where Nairobi is concerned, I'de suggest only a matter of time and Dar Es Salam will have the same sorts of issues in this regard.