I would rather take several hunts, as opposed to a "once in a life time" hunt, because I don't know of anyplace you can go in Africa to be able to take every game animal in which one might be interested.
Plus, I think most first time hunters would be so overwhelmed with only one 21-days safari, that they would want to shoot the first thing that came along, and completely miss the total "African Experience."
(Almost anyone can pull a trigger)
To me, researching, planning, choosing hunts and rifles, talking with PH's, working up cartridges and loadings, and reading at least a dozen books, is (almost) as much a part of the hunt, as is the actual hunt.
To me, I would have a "hollow" feeling just showing up with an outfitter at the Selous Game Reserve with a .30/06 and a .458 WM and expecting to experience the "African Adventure of a Lifetime."
Especially, if I had to hunt with rented rifles - the safari would mean even less.
So much of the total experience of African safari hunting would be lost, unless I was the only person (or an equal person in my party) doing all of the research, planning, communication, etc.
I would have little interest in being the "bystander" while someone else made all of the arrangements.
Of course, I would go, if someone else were picking up a significant portion of the tab, because, at least, I know enough to start doing my own research and talking with fellow hunters (on this forum) who could provide guidance.