As I travel to southern Africa very regularly, know exactly where I want to go and have often been there before, I usually do it all myself.
On those occasions where I feel I need expert help, I use a local TA in JNB. The agency is specialized in safaris/game viewing/birding/personal guiding, is very professional, and I know the guy who runs it personally. I therefore know that I will get exactly what I want at a good price.
Johan