Both airlines are excellent. There are still some differences:

- I like the layout of the CX cabin better than the SQ cabin. When travelling alone row 2 is ideal. Lots of space to put things along the windows, far enough away from other passengers. When travelling together row 1 is ideal. Even more privacy/quiet, but still close enough to talk. Row 1 os also a good seat on SQ when travelling alone, but it feels less private.
- The CX lounge in HK is far superior to the SQ lounge in NRT. In SIN and LAX the lounges are similar. But: The CX lounges open fairly late - you have to wait up to an hour for the lounge to open when you arrive on the early night flight. Btw: you need to leave the plane at NRT and take your luggage with you.
- CX has 3 flights with F from LAX, SQ only the one via NRT - so it seems to be easier to rebook on CX and also to find a flight which fits your schedule.

But again, marginal differences when compared to other airlines on this route in F.