yea Turoa has some good wide open slopes and some nice valleys etc so will keep ya interested.
The north island fields are bigger however less reliable for weather, you can go there for a week and only get 2days in, where as down south ya more likely to get 5/7 days, however this is just from my experience.
I havnt been to the queenstown fields so cant give advice on them sorry.
Mt Hutt has a good base and is definatly a good field for intermediate riders, it has wide open slopes of varying steepness, some chutes and drops. a halfpipe, a park (3 kickers and various rails) and a mini park which is just different rails etc and they often have some smaller jumps down one of the green runs.
I would definatly recommend Mt Hutt for an intermediate rider, spent a season there in 06 and it was mint.
only downside is it is not as big as those up north, but if you planned on travelling a few of the fields down south then this wouldnt be a problem as theres more than enough to keep you from being bored.
but yeah you should definatly consider Cardrona, it has mostly blue runs and a very progressive park.