Can't go wrong with either. CX would be through LAX, SFO and YVR and transitting in HKG (I imagine LAX is preferred). SFO is supposed to get the not-very-good old BC seats most of the time. JL would be via NRT and flying from the same gateways. IIRC, the JL flights generally leave N. Am. in the mid afternoon and arriving NRT late afternoon while the CX flights leave late evening (except for daytime YVR flight) and arrive in HKG early morning. If the JL itinerary forces and overnight, the airline wil provide accomodation in NRT on request.
If you can leave by 1 January and come back by 15 January, you can go by NW business class cheap. Strangely, it doesn't seem to be available from LAS, SEA, SFO and LAX for a variety of date but if you leave from Vancouver, it's US$ 1,870 inc. taxes and fees. Shows but not bookable on NWA.com; have to call to book. Itinerary is YVR-SEA-NRT-BKK-NRT-HNL-SEA-YVR. I am traveeling 31 Dec/9 January.