Both of those countries are fab. I love them both. Whichever you choose, it won't be a bad decision!
But if I had to choose I think it'd have to be NZ. I love that it's just like England, but even more English than England, in a funny kind of way. It's what England should be like.
And there's lots of space, hardly any people, they drive on the correct side of the road, amazing countryside, there's subtropical weather up north and there's no nasty animals.
Australia is very cool too of course. It a young, confident nation, and perhaps on its way to becoming a world power. The people are so friendly, the weather is great, and it's still quite Englishy.