Where you go depends on the season, because the rains determine migrations and where you can see animals, as described here. Everywhere is pretty good in December, except Zimbabwe (I would suggest that Zimbabwe has bigger problems than weather though!).
Countries I’d recommend safaris from personal experience are Tanzania, Botswana and Namibia. I’ve never been to Kenya. Kenya is nice, but some argue it’s kind of overdone. South Africa, I found, is very Disney like as you have paved roads running through Kruger that everyone can just drive on themselves sans guide.
If you are interested in just a Safari, Botswana and Namibia are fun and not overrun with tourists the way the big parks in East Africa are. The Okavango Delta and Chobe in Bostwana and Etosha Park in Namibia are so vast and really rich with game. You’ll see great game here, but these countries don’t offer other experiences like snorkeling in the Indian Ocean or seeing Victoria Falls.
Zambia is lovely, especially if you want to see Victoria Falls, but it may not be the right time of year to see game there, but if you wind up in Southern Africa do consider flying up to Livingston to see the Falls.
And Tanzania? If you want to hit a stunning beach and/or hike a mountain in addition to your safari, there’s no better place. Here are some posts from past posts:
I arranged my travel through a outfit called ATR in the UK. They were great considering all the things we wanted to do and the internal flights we had to book.
Agree? Disagree? Curious to know what people out there think!