Realistically, you can visit New Zealand at any time of year, and there will always be something going on to entertain you, and the weather throughout the year is never too bad, particularly on the North Island.
Winter is the best time to visit for skiing, and often you will find that the hotel rates in the cities are much lower than throughout the rest of the year, while in summer, beaches are filled with tourists, and there are many parties. Christmas tends to be very busy, particularly with families, and the prices are higher. You should book your flights well in advance if you are travelling at peak season.
