The only idea I have is a question - is there any possible way you can stay for longer? 10-14 days doesn't sound like enough time!
We did a motor tour of both islands over 6 weeks (4 weeks south, 2 weeks north) so if you already have a fair idea of the sort of area you'd like to live in (town vs rural, city vs town, Auckland vs anywhere else etc) then that might help narrow it down for you? Definitely spend a few days in each place that you'd like to visit, otherwise it becomes a blur of driving and you don't get to enjoy much.
I would probably stick to just North Island on that timescale, I'm sure someone who lives there can give you a good idea of where to spend Christmas/New Year. Have a great trip!
EoI in: 5th June 2008 (150 pts, no job offer)
ITA rec: 7th August 2008
ITA back: 30th November 2008
Job offer: 10th January 2009
Arrived: 19th May 2009
Loving it: all the time!