I try to use OZ because there miles don't expire and their Elite requirements are favorable. (Renewal and *G)
However, not all *A low fare classes credit to OZ at 100%. Indeed, I have not found any airline in any alliance that gives full credit for all partner low fares...
But UA seems to have the best policy for low fares, so I use them to credit those that OZ doesn't give 100%.
Being down under, you will have to be careful to have UA activity every 18 months to keep the account active though.