Depends on what you're trading out F for J for., and if you've flown CX F before. If you havem't flown CX F, then stick with F, even with the YVR stop. CX F, to coin a phrase, is the stuff that memories are made of. And if the choice is between the 9-ish PM connection over YVR in F, or the 1-AM ish nonstop in J, go with the YVR flight. What are you really going to do in NY between 9:55P and 1:30AM? Might as well be on a plane drinking Krug.
On the other hand, if it's between the 9:55P and and one of the morning or afternoon nonstops, it's a tougher call. If you've flown CX F before, then you might want to flip to one of the earlier flights in J. I like those timings better But for me it would be a hard choice because flying F transpac is still special for me and CX does it so well. And the timing for the long hop from YVR to HKG is perfectly timed for a nice long sleep if you're on NY time.