Originally Posted by JJeffrey

I would book it through BA but get on the AA metal DFW-LHR flight, then upgrade the LHR-JNB flight with avios.

These days there's hardly any difference in the AA soft product between F & J, if you luck out and an AC agent can pull off an upgrade to F then great, if not no biggie as you're still in 77W J which is about as good.

I haven't been following how BA is coming along with their business cabin updates, but there's a huge difference between their awful old business class and F, so that is what I'd prioritize by booking through BA.