Unfortunately the AA LAX-AKL does not operate in September this year. Premium Economy on both carriers is very similar. I have a slight preference for the 787 but you'll only find that from LAX on AA, and LAX-MEL on QF on certain days when they run a second flight on that route. It may be more convenient for you to route via DFW onto the Qantas A380 DFW-SYD flight. Looks like that operates daily except Tuesdays in September.