First things first.....

Ostrich and

Ziegfried
Ziegfried, what you say is really scary! I did NOT know of the latest news about the USA.

Ostrich, it's certainly a difficult choice you have there. From an immigration point of view (solely paperwork and so forth), the USA would for you guys be the "easiest", seeing as you are already American. And there IS a lot more opportunity to grow careerwise for IT people.
On the other hand, politically speaking and looking at what is going on in the various countries, NZ certainly looks like a good option.
One has to take so many things into consideration though.
We're a bit worried about finding jobs, expensive housing, weak education system, and the "no tall poppy" thing. Is this really an issue for many of you?
For some, these issues are a genuine concern.
IT would mean you have the choice of Auckland, Hamilton, Wellington, Christchurch as your main possibilities, and not necessarily in that order (I just listed from North to South). That is not to say that you won't find IT jobs anywhere else.
Salary-wise, you'll earn more in Auckland, but then again, housing is more expensive there.
The "Tall Poppy Syndrome" is real, even the Kiwi's are aware of it (we even had our pastor preach on it once - about people should NOT have that attitude!).
Education can be a problem depending on what you're expecting from it. This is an issue anywhere in the world these days (my opinion). It has gone downhill because those in high places want the masses dumbed down so they can control them better. I homeschool now.

I myself, and my family lived in the USA for 9 years before moving here. I got spoiled rotten there!! It's the land of convenience for sure!! But as Ziegfried has said, things are going downhill there fast, and I can only say that right now, I'm glad that I'm not there. I have some American friends there that have contacted me, and asked about immigrating here because they're very upset about what's happening there. Unfortunately for the one couple, they are too old to do the move.
On the other hand, I see how NZ also has made some "interesting" moves... they sure look like they are just about in bed with China themselves!
At the end of the day, it's still gotta be your decision, because it's your life, and your children's future. I'd say it's a serious prayer-issue, if you're a praying person!