Oceania (Australia, New Zealand & the South Pacific) - ANZ Premium Economy or UA Biz US to Syd?

Hi. We're going on our regular trip to Australia this year from DC. We usually book with Air New Zealand because of their premium economy and the superior performance of their FAs, especially as we travel with children. (They treat our son as if he's an important passenger, in contrast to the usual unenthusiastic/negative reception we get on UA.)

We heaven't flown the new PE seats on ANZ. Neither of us is tall (5'8") and we've slept well in the old PE seats.

We are both Premier on UA and have enough miles for upgrade to biz. Which would you recommend?

If you can be guaranteed an upgrade at the time of booking UA biz definitely.
Going in the upgrade lottery is another matter
Other options are Delta, Virgin Australia & Qantas to SYD

Now the pitch has been improved the new PE on Air NZ should be better than the old PE, as long as you can get the inner seats and not the outer seats.