Award in F returning HKG-LHR

CX is not available but BA and QF are - so simple question - which would you pick?

I have travelled BA F before and while it was fine, I thought it was a big step down from CX.

So how does QF compare to BA and CX?

If the CX flights become available, I am planning to change the ticket and pay the re-isuue fee - do you think its worth it?

Many thanx