We have lived in both countries and from our own PERSONAL experience, Australia (specifically Melbourne) offers double the income of NZ, lower costs, miles better lifestyle etc etc
One immigration trap to be aware of btw is that if you enter NZ as an Australian
PR, your time in NZ will not count towards Oz citizenship. Therefore when your Oz
PR runs out 5 years after being issued you will no longer be able to live in either country unless you apply for another visa.
Buzzy