VroomVroomVroom - www.vroomvroomvroom.co.uk

I've used VroomVroomVroom for car rental plenty of times in Australia, and they're just as good in New Zealand. The website is quick and easy to use and lets you compare all the major car rental suppliers on one screen (Avis, Budget, Hertz, Europcar, Thrifty etc). I've even found them to be cheaper in some cases. Apparently they also compare campervan rentals, but I've only used them for cars. I've also used their live chat support a couple of times and found them to be quite helpful. Will definitely continue to use (and recommend) VroomVroomVroom.