If you live in New Zealand, you're probably stuck with Airpoints as your "native" program.
United is known to be most generous with mileage earning on discount fares, but this does not necessarily apply to their partners. Searching for the Star Gold comparison chart might be a good place to start. It will lay out benefits, and to some extent earnings, for each program. Then you can look for individual program details concerning the fare classes you are most likely to fly (for instance, if you fly NZ most of the time on "S" fares, see which programs give 100% mileage, which give 70%, or which give zero. Made up example, obviously).
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