No answers! I've never taken either route in first, but the other consideration could be whether you are likely to be sleeping or not.

As I rarely fly F, I take the view that if I'm going to sleep for most of the flight, I might as well just fly in J, as you miss out on the service elements. As such I tend to prefer "day" flights where I am not tired, stay awake for most of or the whole flight so I can enjoy the full service. Just something else to think about, and would probably tilt things in favor of LAX-NRT vs NRT-LAX for me.