Hi Sarah,
Would it be possible that you could try out one of the cities first and, later on, be transferred to the other if you aren't that settled? It might be worth asking the HR person if that was an option seeing as they can't make up their own minds about where they want you. You could have 2 bites of the proverbial cherry then
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People seem to vary regarding their thoughts on Auckland. Some love it, some hate it. Probably the same goes for Wellie. As Beth says, Wellie is nearer to the SI and all that it has to offer. Both cities are on the water. I know there is snow in the centre of NI in winter but I'm not sure if there's skiing there.
Difficult choice and one I hope you can come up with an answer for. Good luck with it and well done to your hubby for landing his job AND a choice of which city to live in (although that may seem more of a curse at the moment than a blessing).