My gut feeling is AA - sign up for a Plat Challenge and you'll do well. Generally, AA are hard to beat for miles, especially when you've got a bit of status (you'll prob be earning at the Plat rate by the HKG-LHR flight!) - and the Plat status sort you out with lounge access when flying QF.

There's really only one way to determine things though - get your calculator out. Hauteboy's OWE validator should help as well.