We had a very good experience using Omega for almost a month in November 2009. The car was older but was well maintained. No issues with agency upon return of both cars.
Would recommend them for NZ!
Are you US based? Be careful with depending upon your US issued credit card providing rental car insurance. Amex does not provide their automatic CDW in 'wrong-side' drive countries like Oz & NZ. I managed to locate a Visa card from Charles Schwab which did but don't think that that card is available any longer....