A top-rated safari country has a great variety of safari circuits, offers safaris for all interests and budgets, has beach extensions, provides great wildlife sightings and has something nobody else has.
All that applies for example to Tanzania. It got its popular northern circuit with the Ngorongoro Crater and the Serengeti and off the beaten track safaris in Selous and Ruaha. It has the Great Migration including the calving of the wildebeest and great wildlife viewing in the other parks. It got the best chimp tracking in Africa in Gombe and Mahale Mountains and fabulous beach extensions on Zanzibar. The only negative to say about Tanzania is, that it is not possible to put all that in one safari. One needs to come back and back to see it all, which is not an unpleasant thing to do.
Similar lists can be made for other destinations like Botswana and Kenya. Look out for them and find the African safari tour that includes all highlights you want to see.