I'm going echo the opinion that New Zealand's North Island is spectacular. Between Maori culture, glow worm caves, zorbing, the best indian food I've ever had (in a corner shopping mall in Hamilton, no less), earthquakes ... just amazing. Auckland wasn't particularly spectacular, but the rest of the drive down to Wellington was so good. I wish I'd spent more than the 7 days I did.

That said, Australia's big cities are pretty good in their own right, but it's not the vast expanse of nature and 'Wow' that New Zealand is.