This will be a horses for courses question...
Assuming Biz
Cathay - Best staff in the business. However seats dont fully recline and are such an angle you do slip down over time while sleeping. IFE OK but has a fiddly handheld thing but is very good. LHR lounge OK but HK lounge veru good
I fly 150k miles a year with CX out of preference of the other 3 solely due to the quality of the staff.
BA - Lie flat and good amenities, To generalise staff not so helpful and you will feel as if you are putting them out of their way by being there on some flights. To be honest every time I fly them for whatever reason I wonder why I didnt take one of the other two
Virgin - Lie flat with a long bed. Good amenities/IFE and great lounge esp on return back to Heathrow with the after flight facilities. Staff can be a little 'too cool' for some but in general are very good. Food of choice sometimes runs out which can be a pain but not a major prob...