Hi There,
Renting car / campervan?
I rented from Nationwide Car Rental during my visit last May. They have a very good customer service and the most important: relatively new and reliable cars. They even give me a good discount.
I rented a Corolla Kanagawa and I am fully satisfied. Don't forget to rent the GPS unit... It was VERY helpful to help you navigating NZ.
They also have free airport pickup and drop off, and you can also rent and return in different location.
For campervan, try ACE rental.