Hi johnathome, welcome to FT.

Assuming you are travelling on a DONEx or a DGLOBnn, I'd suggest taking QF. I feel, it's better to have confirmed bookings.

If it helps any there are reports around that the London based crew who normally operate the LHR-HKG route on Qantas are among the "best" for service.

Other than that, there's a few threads around about the differences in the products but IMHO there is little between them.

Certainly any perception that CX may be slightly better would not be enough to stay with in your situation.