NH don't fly to SYD.

The recommendation for OZ was for convenienece purposes, although admittedly having just checked the routes on GCM there isn't much in it!. SQ only have regional seats to PVG so there's no additional 'comfort' available in flying them than the other options. NZ have the best seat product available with their excellent Business Premier to AKL so probably worth the extra to fly with them.

I have flown OZ (and NH) regionally in S.E. Asia and found both to be pretty decent. While they are not up to SQ standards but they're better than many others.

It's down to the OP to decide what they really want to get from the trip. I say this as someone who has done more than my share of going out of my way to fly SQ in recent years !!.