Southern Lakes Helicopters, is the company in Te anau
The one down the West coast, probably Fox and Franz Helicopters. Also Glacier Helicopters and The Helicopter Line operate down the coast.
personally i would fly with one of the above. you could race around and go for the cheap guy that cant afford to put a turbine on to take you to 13,000'. but myself i would pick the guys that have been doing it for 20 or 30 years in 500's 206s and as350's.
I went up in an R44 with Southern Lakes Heli's. As far as I am concerned, it was the best trip I did there.