I'm currently working in Austria, as an instructor... I would like to do the same in the summer season in the southern hemisphere, but i would like to choose based on the powder conditions...
Which are the best powder resorts in the the South?
I would look at places like Valle Nevado in Chile and resorts in Argentina. You can actually get some goods that are wind sheltered vs what is offered in New Zealand (which wouldn't suck either). Especially in Argentina. I have seen a lot of good footy of people riding stuff in the trees there. Tree riding=wind sheltered=more powder days...
New Zealand is great but for reasons of what else there is to do in addition to snowboarding (eg paddling, climbing). For the most part (I've only been to Remarkables and Cardrona) there is a dearth of "trees and steeps" type of terrain that make powder riding all the more enjoyable.