Seconded, thirded, fourthed and fifthed.

I live in Chch and the only reason I'll ever depart ex-Auckland is because a) there is no other option for the schedule/timings I need, or b) because I want to try and use some upgrades.

Chch lounge is much nicer and less crowded, the terminal area is more pleasant, security and customs is faster (last time I departed through Auckland airport in the evening there was a nearly 45m wait to have your bags searched if they triggered the scanner machine ... I know as mine was fine but my travel partner got stuck in the queue)

Singapore airlines morning departure time is very genial, and you've also got the option of the evening Emirates departure. On Air NZ presumably you'd be codeshared on the Singapore flight anyway.

100% I'd never go through Auckland international unless it's the only way I can travel or use my upgrades and not feel I'm wasting them.