I agree with gleff's comments michswiss, I understand you do plenty of flying with OW, but in this case, achieving status, the upgrades and the price of awards makes UA the sensible choice.

The status bonus miles they'll earn on UA metal will be valuable (i'm not sure what the deal is with flying NZ metal with a UA flight number?), the comp upgrade certificates. Sure achieving status is harder than AC's program where you only need 35k to hit *G, the extra miles, the slightly lower priced awards, and upgrade certs for UA flights will be worth it.

As said, achieving or retaining status on NZ is a tough slog now and I find NZ treat other *G's as well as their *G's in their own program (with the exception of NZ Gold Elites). They will also really appreciate the 34" pitch in Y flying across the pacific against what QF have to offer. QF do offer IFE on their 744's across there, but NZ is still a good product with great food, great service, roomy seats and very new movies on the screen. NZ also block off the exit row seats in rows 23 and 35 for all *G, NZ *S and Koru flyers. Exit row 45 is a free for all.