Look at EK. (Usually) good flight options, SC (on QF codeshare) and points earn , decent lounges.
I would second this recommendation if possible. As a QF Gold you'll have access to Emirates lounges throughout your journey. If ticketed as a QF marketed flight, in theory you should earn similar status credits as a QF operated flight. In addition, Emirates flies to more locations in the UK than BA or QF including Birmingham, Manchester, Newcastle, Glasgow and Edinburgh aside from the London airports of Heathrow, Gatwick and Stanstaid which depending on your final destination in the UK may be more preferable than flying into Heathrow which can be chock-a-block at the best of times.
In terms of other OneWorld partners, yes you will earn status credits with them albeit you may earn less depending on fare class and airline. Personally, I'd be tempted to fly American over to LHR since those fares by definition must be discounted due to the "inconvenience" of having to clear US immigration, customs and security at a hub like LAX. On the other hand, Qantas and American have a tight partnership meaning you'll likely earn the most status credits and points of any OneWorld partner. In addition, the slightly circuitous routing will likely result in additional status credits coming your way. Indeed you could engineering some particularly unusual routings in the US to attract additional status credits like SYD > LAX > DFW > MIA > JFK > LHR. Whether it is worth hopping through all those airports just to earn additional status credits and clear out the buffet at AAdmirals lounges, I'll leave up to you!
Since by definition you'll need to connect at least one airport, connection airports are another key consideration. Personally, I'd prefer to connect at an LAX or worst case scenario SIN than say CMB or DEL where the transit process is known not to be as smooth.
Another key consideration is what cabin you will be booked into and what fare class within that cabin you are booked. For instance a flexible fare will likely attract double the status credits as a standard fare. As you book closer to departure, generally the deep discount economy fares go away, in favour of more pricey flexible fares, which should work in your favour. In addition, those flexible fares are easier to upgrade into Premium Economy, BusinessFirst and Global First using points on QF. Similarly Premium Economy will attract more status credits than an Economy.
-RooFlyer88
