Hey i've lived in Wanaka most of my life and it really depends on the type of skiing.
For terrain and powder and big mtn skiing, treble cone(wanaka) is THE best mountain in NZ without a doubt. Huge advanced terrain, not busy, and just super fun to ski at. Heap of good big mtn skiers there, and over in the saddle no problems with bad skiers getting in the way. Apart from park skiing, my favourite resort in NZ by FAR.
www.treblecone.co.nz
Cardrona (in wanaka too) is ok, would be a good resort to teach at but pretty mellow/boring terrain compared to TC, but it pretty good for all around as its got a good park,pipe,some steeps and lines and groomers too.
Remarkables (queenstown) is also sick.A lot like cardrona, not nearly as good as TC in terms of terrain, but has good all around. Decent park,ok steeps ect.
www.nzski.co.nz
Coronet (queenstown)- I'd avoid. Average terrain, park, its low,,bad snow, busy...
Snow Park- I know you can't teach there but definitely sick to check out. Im sure u know plenty about it
Clubbies(cheeseman, craigieburn,broken river,porters,mt potts...) in canterbury are all super sick. Generally no park but knarly as terrain and SUPER quiet. Check chillout.co.nz
Ohau- almost a clubbie, near canterbury sick terrain. Small. Chill
Oh and btw all these are in the south island. Wanaka and queenstown are close together in the tourist center i guess you would say.Canterbury is a fwe hours north. Those are the two areas i would look at mainly- def get the best snow, atmosphere and vibe.
For theski/party life Wanaka/Queenstown for sure.
Want any more info on NZ feel free to PM me