I would say, it would either be the A321neo borrowed from JQi and repained.
Or an A220 new.
Wouldnt be my beloved older bird(y) A330 or newer B787, thats for sure.
Seeing AirNZ uses the narrow body as well from ADL - AKL, most likely QF will do this too, ie, the narrow body, maybe 3 days a week.
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At least now, when it starts, there is the/an option of paying for J ADL - AKL (direct), either for the space, or because your employer/payer is paying, better that being stuck in the middle of the A321neo/A320 that AirNZ flies ADL - AKL.
Or buying a comfort seat booking on QF.
Or the fact that QFF points dont expire, so long as there is activity, vs AirNZs Airpoints $ that will expire, 4 years after accrual, and can only use it for seat selection, cant use Airpoint $ for part fare payment, for us Aus residents, think NZ residents can do part pay, ie, 20% points and 80% cash/card.