Genetic drift IIRC is a side effect of time. Africa would have the largest diversity because the multiple groups that didn’t leave Africa are all in their own corners, lightly stirred, and drifting. Collect all the African inhabitants, try to backdate them, and you’ll have a pretty good picture.
If one small group leaves Africa, they drift too. But everyone beyond the Red Sea probably only drifts from that one group, does not include the other diverse groups who stayed behind in Club Congo. When the group that left Siberia for North America set sail (by foot?) then there would only be that limited group, and they would only accumulate 24,000 years or so of diversity.
So I assume diversity reflects the size and variety of the initial group, plus the amount of time to drift, modified by changed environmental pressures - skin color, etc.
But if we assume the least variation happens with the peoples associated with the African plains where we assume we mostly evolved to our present form(s)… That would be Kenya. No wonder a Kenyan is the most important most powerful person in the world today.
But seriously - original populations can be displaced, frequently are, if the displacement group has better tech - agriculture or domestication, better weaponry, adaptions, etc. So without a deep study of early human migrations about Africa, it’s hard to pinpoint your answer.