Options to JNB
From the US one option is to try to go to GRU and then from GRU to JNB on SA in business. Fairly good availability of business seats for 45K miles one way. Very poor availability for discounted business from USA to GRU but good availability in coach. 30K each way.
I flew this route last year and was fortunate to get a business on all legs. United business is a decent product, obviously not like Emirates or Singapore(by reputation only, I have not flown but have used the Singapore Silver Kris lounge which exceeds anything I have experience in a US business lounge, their Gold Kris lounge is unimpressive). Ethiopian is decent in business, not as nice as United. Food is ok, does have alcohol which Egyptian does not. I strongly thought about booking Egyptian for my trip next year but decided to bit the bullet and fly revenue coach to GRU and back and use my miles for business on SA between GRU and JNB. I need the miles to stay 1K. I wasn't real keen on a completely dry flight for 25+ hours so that was the reason I gave back the Egyptian tickets after I got them. Also disadvantage that Egyptian flies out of JFK and that means a shuttle van ride to EWR for United connections. Ethiopian has option of Ethiopian food in business. Interesting and worth trying at least once. However for me not more than once.
12 hours Zombie class on United from USA to GRU is not fun but doable. I intend to sleep on the SA flight and I think the SA product is fairly equal to United business. Wine list on SA is probably better than United. Food is equivalent or just a bit below.
I found it very hard to find any flights business on discounted miles from IAD to JNB. SA does have such a flight.
The business lounge for SA at GRU is very nice. Better than most United Clubs. Only the United Hong Kong Club comes close.
Ethiopian business lounge is decent.
Bottom line is if you want all business, go Ethiopian. If you want nice and can get business from USA to GRU then the SA option is good due to the good availability on SA. If you want best availability in business on any airline, then Egyptian. The former president of SA was on an Ethiopian flight I took back from JNB two years ago so that should tell you it is a decent product. I don't think I would want to be back in coach however. If I had to be coach all the way on miles, then probably United to GRU and SA from GRU to JNB.