AA would seem to be much the better bet for redemption value of the earned miles.
If deperate for OWE status could consider crediting to BAEC (noting you are in London) as your trip should get you there provided you ended up with 4 BA flights in that membership year. The BA points would normally prove more valuable than QF ones (but again less than AA).
3 reasons I can think of to go for QF: To consolidate your points for a One World RTW Awards. Plat would help in securing QF upgrades if you were planning to fly much with them in future. If lifetime status on QF is feasible and desirable