Agree with chasgoose whichever flight you can get a seat on. Just to clarify, you're flying out of HKG correct, not JFK/LAX -> HKG? If so then it doesn't matter which flight you take for lounge purposes. Just make sure you have time at the airport to check out the Pier and the Wing first class since this will be your first time experiencing first.
I use to live in the west coast and would fly back to SFO, but now living in NYC. I've found the flight time difference between west coast and JFK has definitely been greater than 20 minutes. HKG-SFO flights in my experience were usually around 12 hours, HKG-JFK is a good 14 hours.