I did NZ to USA back in Aug 2012 in J, and combined with being VA Platinum, was well looked after.
MEL-AKL on 773
AKL-SFO on 747
LAX-AKL on 773
AKL-SYD on 773
The upgraded J product on 773 cf. 747 was far better: bedding, IFE. Just small things were better.
Entry into SFO was great: didn't wait at Immigration at all. Though I've never arrived into LAX, so can't compare.
Had a VX flight SEA-LAX before my LAX-AKL flight, so had to exit terminal (T3?) and go to check-in (T2?) to get boarding passes. (Never found out if this was the right procedure, but SEA VX assured me they couldn't issue my boarding passes.. I was skeptical). Luggage was tagged from SEA-SYD, though wasn't surprised when I got to SYD and bags were still in LAX (was annoying, as I had separate flight through to CNS on QF when I arrived into SYD. Fortunately, QF handle NZ's lost baggage in Oz). Considering I had to go to NZ check-in anyway, I should've just got luggage from SEA-LAX, and checked it myself.
My first experience departing from LAX was painful, compared to departing Australia, that is, though I get the sense this is typical of USA. They closed the Priority Security lane 1 minute before I got there, and wouldn't let me jump over, so took ages to get airside. NZ Lounge was busy and crowded, so not a relaxing place to be.
NZ J was great service and product. As VA Platinum, seemed to get extra attention, especially on the TT sectors (e.g. got asked meal choice before other pax around me, greeting from CSM).
Transfers through AKL both ways was easy and pain-free. Enough time to use the showers in the AKL Lounge, and the shower facilities were great. Lounge was pretty busy both times too, but not as much of a zoo as LAX.