I flew twice JFK-HKG. I tried the 1AM flight and the 9AM flight.

I think the answer to your question depends on what you want to do when you arrive in HKG. For me, my end destination is Shanghai or Jakarta. So regardless I arrive in HKG at 6AM in the morning or 2PM, I will lose 1 day already by the time I land in Shanghai/Jakarta. Therefore, I prefer CX841 because I arrive in Jakarta/Shanghai late afternoon/early evening. It gives me enough time to stretch a bit, eat dinner, and go to sleep during normal time.

Yes, you lose 1 day in JFK but i find it easier to get rid of jet lag this way. Btw, depending on when you fly, it's not all day light. As mentioned already in the previous post, above North Pole/Siberia you will get darkness