MRSTARALLIANCE, some important differences between UA and NZ programmes (I, too, am a member of both) are:
1. NZ is based on kilometres, UA is based on miles; hence both earning and burning rates are higher for NZ. There are 1.6km to a mile, so on that basis - although of course it is not quite that simple - NZ-Australia flights are actually cheaper on NZ since 1.6 x 20,000 = 32,000.
2. On NZ, the business-class 25% bonus counts as status miles, whereas on UA it does not. Given that you're flying business class, if I were you I'd put the points on NZ.

Assuming that you meant to write 29,000 miles rather than km (I'm not sure you can get around the world for 29,000km - not from NZ anyway), your itinerary would earn you 58,000 NZ AirPoints (29,000 x 1.6 x 1.25), *all* of which count towards status, or 36,250 UA M+ miles (29,000 x 1.25), of which only 29,000 count towards status. This means that on NZ you're only 2,000km away from gold status (60,000km is the threshold) whereas on UA you're still 21,000 miles away from the 50,000 mile gold threshold.

Of course, if you were in economy that would complicate matters since NZ only credit 0.7 points per km in discount economy. I can't comment on the other * carriers FF programmes, but given that you already belong to AirPoints (and presumably have some points with them already, so you may hit gold on this trip) I'd stick with NZ.

Hope this helps - and enjoy your RTW! (I'm sick with envy.) Where are you flying, and with whom?