Regardless of aircraft, I'd pick F over J every time - BA F may not be perfect, but it's just nicer than J however you cut it (in my view) - especially for a nice long flight like JNB where you will have time to enjoy the CCR and the meal and then a decent night of sleep.
F on the 747 is also quite special, in the nose - at least try it. Club World on the A380 will be around for years; F on a 747 probably not.
no contest