Type of aircraft not critical. This is rather a once-in-a-lifetime trip and in all honesty, COST will be the deciding factor when it comes to the flight.

Anything that I save on airfare will be invested in making the experience whilst there more memorable. I'd rather remember the safari than a luxurious ride on an airplane.

Oddly enough, the most direct (Atlanta to Joburg, Joburg to Windhoek) seems to be by far the least expensive.