The A350 is a more confortable passenger experience and notably quieter.

I've only flown CI on their W product but it was on the A359 which is wider than the usual W config at 2-3-2, but the 77W is 8 across if I recall correctly. The soft product was fine, but unremarkable.

Depends how much you value the better product on JX, and whether you have a preference for Skyteam for mileage or status.