Did AKL-SIN-AKL in PE just a few months ago, AKL-SIN with NZ on 789 and SIN-AKL with SQ on 359.

I have to say hands down NZ wins by a wide margin. NZ PE is 2-3-2 whereas SQ is 2-4-2 and that made a massive difference. Service-wise you get a differential offering from Y with NZ (premium dining, overnight pack, separate bathrooms), but with SQ it's virtually the same as Y (same food, no overnight pack, sharing bathrooms with Y which is a massive letdown).

Edit: Although I see you are flying as a fam of 4. Maybe the 2-4-2 layout on SQ is a better fit for your group, but I think you can spread the group across two rows of two on NZ