The South Island of NZ was some easy driving. Good roads and no traffic. Sure, it's the "wrong" side of the road if you're from the United States, but I found adoption to be fast and easy.

It was actually harder for me coming back home and getting used to driving on the right side than it was for me to go there and get used to driving on the left.

My driving in Australia was limited to Cairns to Cape Tribulation and back, which was also a very easy drive. I'm sure Sydney, for example, would have been a much different experience. I did notice that drivers in Australia handled traffic circles with much more aplomb than I've ever seen here in the States.