I would not do EK or SQ - neither guarantee flat seats on all legs. on EK the business class seat pitch is worse than SQ too on many planes - while EK can be good there are so many seat configurations it takes a lot of planning to get what you want and then the connections in DXB sometimes don't look great.

CX has the worst flat beds of any airline I have flown on - the most narrow and hot and sweaty due to poor air circulation and no individual vents.

I would choose either BA or VS, my personal preference is VS and the A346 it uses SYD-HKG-LHR is a very smooth and quiet ride, 747s can be incredibly noisy!

Lots of reviews will compare the two, a personal summary is:

- BA more formal, professional crew - tend to be older vs VS younger and more relaxed
- BA often reported to have better food vs VS but I think VS is getting better, VS is dine when you want to
- people like the BA seat that reclines fully to become the bed vs VS version which flips over
- VS has I think more space and since all seats access the aisle directly, you don't disturb anyone
- both have good IFE, I think the screen is better placed on VS
- don't know the VS lounge at SYD but HKG is good and LHR is excellent, the best in the world
- VS on board bar is wonderful as a place to chill and meet / talk with other pax and crew, BA has the kitchen