Another issue you'll run into with Mileage Plus is the requirement for 4 segments per year on UA metal. It would work easily if you fly UA to the US then have a connection, but if you're flying NZ or SQ to the US, how many domestic flights are you taking each year? The lack of lounge access also is certainly an issue if you have domestic flights not part of an international itinerary (same day). That part doesn't affect me because I extremely rarely have domestic flights that aren't connecting to an international flight.
OZ, TK, A3, and MS all have advantageous ways of qualifying for *G, but make sure you take your earning ratios into consideration. Some programs like TK and MS are notoriously slow for updating earning charts when a partner airline changes, so may not have any earnings at all on UA's new Premium Economy product for example, ET's P fares are another ridiculous example where only CA added them when ET introduced P fares for paid discount business class. There's a great website:
www.wheretocredit.com that allows you to enter the fare class and airline you're flying on and shows you the earning on each partner's program.