SNAP rentals in NZ gets consistently very bad reviews on Yelp and Tripadvisor.

A previous poster recommended Ezi Car Rental. I don't know this company but trust the poster knows what they are talking about. I personally have rented from Omega a few times and been happy, but if you were to consider them, make sure to pick a newer model car (they list their car model years on the rental page).

Also, when you pick up make sure to ask whether there are any roads you are not permitted to drive (i.e., are not covered by insurance). There are a couple of unsealed mountainous roads that some companies don't allow, but you likely wouldn't be wanting to drive them anyway. E.g., from Ezi Car Rental's FAQ page:

Are there any roads I cannot drive on?You can drive Ezi Car Rental cars on any road except:

• Tasman Valley Road – also known as the Ball Hut access road (Aoraki/Mt Cook)
• Skippers Canyon Road (Queenstown)
• Ninety Mile Beach (Northland)
• Any roads north of Colville on the Coromandel Peninsula