mattwnz: I was speaking to a builder/ developer who builds eco houses, and he advised against PVC from his own experience. He said they just don't stack up compared to the new aluminum profiles you can now get. Also questions over low term durability with the NZ conditions. Also many people don't like the look of PVC, they have a bit of a stigma to them. They are used a lot in the UK, and don't look great when retrofitted into terraces . I would suggest visiting some house that have had them in for the last 10 years to see how they are performing, and how the owners find them. With aluminum, they are a known quantity, and durable/low maintenance. I have some anodized ones that were install 12 years ago, and they look as good as new.
That's what many people say, but there's never anything to back it up, and it's not what the research I've found suggests. I already have french doors, another door, and a bathroom window in PVC, the oldest only a few years old but seems as good as new.