I dont know much about Aus, but if your coming to Nz then Wanaka is a pretty good place to base yourself. Its cheaper than Queenstown to stay at, including some backpackers which will let ya stay free in exchange for doing chores around the lodge. or there are the nearby towns like albert town which have some cheap lodges. Wanaka has a decent nightlife...though Queenstowns is alot better.
Wanaka gives easy access to Treble Cone, Cardrona and Snow Park.
The Remarkables and Coronet Peak are only a short drive away (Weather permitting).
Treble Cone - good for freeriding, with a good mix of steeps and chutes for the more advanced and open slopes and trials for beginner to intermediate. Can get quite icey and full of moguls without fresh snow. Also can get very boring if the outter bowls are closed due to weather conditions. Mostly skiers up Treble Cone, and has very expensive lift tickets to try and achieve that exclusive upper class skier only image. Some staff can be pretty short with snowboarders. But still a good time and definatly worth going up.
Snowpark - The name gives it away. This is basically a giant park so if freestyle is your thing then this is the place to be. A good range of features with varying difficulty. If your a park rate this place will easily entertain you for a season. Also has very good pipe. This mountain features in alot of videos, including the new DC mountain lab 1.5. However dont expect a car to tow you around when you go up. can get crowded.
Cardrona - My favourite of the three so this is probably biased but oh well. Cardrona has the best mix of everything. Has two halfpipes and a super pipe, a great park with lots of different features to satisfy your freestyle cravings, then it has wide open slopes, a few chutes, some drops for when your in a freeriding mood. and some good backcountry if your willing to hike. the terrain varies in difficulty so there really is something for everyone. Can get pretty crowded round the holidays, but they have just upgraded one of their lifts and a cafe so this should help.
Havent been to Coronet or the Remarkables but as some on else said the Remarkables have been upgrading their freestyle options and i have head good things. I think Coronet opens the earliest of all the mountains as it has the most snowmakers.
But yea at pretty much any mountain in Nz ya gotta watch for core shots from our shark teeth rocks if the snow is below par. but ive had fun on our mountains for many years so definatly recommend a trip over.
hope this helps.