Lots of good feedback already.
I did that Newark - Joburg route last June on United, w guns. Outbound no issues. On the morning of departure day in Joburg on the return, flight was cancelled with no rebooking by United, no plan at all to get us out of there. Travel agent had to book on us on Lufthansa through Frankfurt to get back home. No help from United at all and I am Premier 1K status which didnt mean jack.
Personally, economy sucks on all of them and if price is same, I would look at any gun concerns (e.g. suppressors through Newark) first, and then arrival time in Joburg and layover time to make your decision. I also like to get out of US first flight as flights within the US seem to cancel more often than the flights to Doha, Frankfurt, etc... Just my take on it. Cheers