Unfortunately, reports recently say that at least some of the LHR flights are of variable quality in F these days. To be safer (on service quality, although in a cabin that most people regard as inferior, albeit with the same seat) try to go for a CX flight served by A340s (although if it really is a day trip then you'll have a problem in that the A340s do the daytime HKG-LHRs and the 744s do the late evening departures).

But personally all other things being equal on a paid F ticket at the moment I would be tempted to try BA and QF again (I've flown BA F recently on other routes and it was OK, but I haven't flown QF F for 3 or 4 years). Maybe I'm just getting bored with CX?