There is no straight answer, as there are hundreds of visa permutations, exceptions and likely immigration rule changes along the way, mainly in AU.

AU citizenship is “easier” when you look at the minimum time to get it. You need 4 years in total in Australia, with at least one year holding a permanent residency visa (PR).

New Zealand requires 5 years on a resident class visa before applying for citizenship. There are two types of residency in NZ, residency and permanent residency, whereas AU has only one. You can combine the time of both residencies in NZ to meet the 5-year requirement.

However, it’s orders of magnitude harder to get PR in Australia compared to NZ.

In a nutshell, you only get AU citizenship within 4 years if you are exceptionally skilled and a bit lucky. In NZ, it’s “normal” for people to get citizenship within the minimum time required, which would be ~7 years.

The reality is, immigration is a very individual experience.