Welcome to the forum,
First thing to do is decide fence or no fence. And if fenced how big? Some propertys are 5,000 acers or less, some are over 100,000.
Second: whats more important? Big trpohys or sweeping vistas. Example in general the limpopo brush country has big horns but is flat and brushy like texas. Not much to see. On the other hand places like the Eastern Cape and Namabia have facinating scenery.
Another thing to consider is the kind of experince you are looking for. RSA is very modern with a high population, cell phones work pretty much everywhere. Not the wild africa you have read about all these years. Parts of Namibia are vast desert scrub with a very low population.
The possibilitys are many, do alot of reasearch !!!
Heres 3 outfitters to give you an idea of the differences:
Infinito safaris: eastern cape
Dries visser safaris: Limpopo
Allen chillers namibia (no fence)