Hi there - we went all in to Tanzania last October and it was the highlight of our life. Highly recommend Access2Tanzania and a private guide. It was worth the extra money.
We also chose Tanzania and Access2Tanzania for our Tour Operator and had a similar (highlight of our life) experience. Can't recommend either highly enough.
A2T only offers "private" tours, where a guide takes you and the rest of your party (just me and my wife on our trip) out into the bush in a Land Cruiser that's solely "yours" for the entire trip. There's no-one else aside from your guide and the others in your party in the vehicle. So, the entire trip is up to you (with your guide's suggestions, of course, on where to go)..if there's something you want to stop and watch a while, that's fine - you tell the guide when to move on. There's really no other way, IMHO, to do a trip like this, and I can't imagine being in a big tour bus with dozens of others where you have no control whatsoever on your itinerary or when you start and stop different parts of your tip. You also select your own lodges and camps. Between that and the private guide, it's truly an entirely "custom" safari that YOU control.
I'd suggest determining when you want to go, then narrowing things down from there. Not sure about the other countries, but in Tanzania, you'd visit the "North Circuit" (Tarangire, Lake Manyara Ngorongoro, the Serengeti) at certain times, and either the South or other areas at different times of the year..that's primarily because of weather - Tanzania has a "wet season" and a "dry season" and the animals manage both differently. We went in the "dry" season (late Sept/early Oct of 2019) and the benefit of doing that is that the animals have to congregate around water sources as it's more limited - so they're easier to find. In the wet season, water is not as scarce and there's less congregating at water holes..the foilage is naturally totally different as well..dry season - far easier to see the animals in the more brown'ish grasses..wet season where everything is green - harder..
We did a 10-night safari (followed by 4 nights on Zanzibar at end of our safari to wind down - safari is hard work!) with A2T and visited most of the North Circuit including Arusha National Park, Tarangire National Park, Ngorongoro Crater, Central Serengeti and the Northern Serengeti. Saw literally thousands of animals including all of the "big 5"..but one of the highlights was seeing The Great Migration in the north, with hundreds of thousands of wildebeest and zebra making their way down from Kenya across the Mara River and onto the plains of the Northern Serengeti. Life changing stuff for sure.
Oh, and the comment above about the roads is spot on - we've never seen anything like Tanzania "roads". Our Land Cruiser was built like a tank, and it's a good thing - because any "normal" vehicle would have been totally destroyed by those roads. If you have back issues or any other health problems, be sure to talk through this with both your Tour Operator and Doctor - it's really rough going most of the time, at least in Northern Tanzania.
Happy to answer any questions that might help..good luck!
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