Bus Travel in New Zealand

"Buy a car in New Zealand," said most everyone who heard we were going there. "Then sell it when you leave."
Everybody does it, we hear. There's a great used-car market in New Zealand. Car-sales and rental websites tailored to the market abound.
We looked at the numbers, but it wasn't for us. First, you have to be prepared to put up anywhere from 1,000 (for a clunker) to 8,000 dollars (or more)  for a used car. Then you have to worry about insurance, and maintenance. You really want to be dealing with a mechanic on your trip? Can you trust who you're buying from? Have you flipped a lot of cars before?
And sure, you can recoup your money in the end. But that's assuming it sells fast. And just when do you plan to sell it to get your money back-before you leave, or after you've gone? You're potentially tying your money up for a while, we felt.
And you still have to pay for hotels, hostels, or camp.
We looked at rentals. It's pretty expensive (still cheaper than short-term car rentals, though). A few camper-vans looked pretty good, but that could be touch-and-go with the boy's particular ways. And don't even look at how much the car ferry costs.
It all seemed like too much bother for marginal savings. We ended up renting a car for about two weeks. After that, we caught the bus.
It was a great choice.
New Zealand has an excellent inter-city bus system. It's convenient, on time, and cheap. It goes most everywhere and there are some fantastic circle routes. We went Naked Bus on the south island, Intercity in the north. Most fares were 10-20 dollars, or less.

Admittedly, there was also a lot of this view.

Most of the time the buses weren't crowded. There were three of us, so we usually nabbed the back seat, if the bus wasn't full. The boy had plenty of space to stretch out and sleep, and we could too.
We only ended up on one uncomfortable bus- though it was a doozy. Six hours, Dunedin to Christchurch. The scenery was beautiful but we were on hard plastic seats, in a vehicle just one step up from  a school bus. But stuff happens, and if that's the worst travel experience we have, great. Most of the buses were those nice, upscale coaches with padded, reclining seats.
The bus ended up being a great way for us to see the country. Cue the tune of  "I've Been Everywhere, Man" in your head:

Dunedin, Timaru, Waimate, Omaru,
Christchurch, Washdyke, Temuka, Waipukurau,
Christchurch, Kaikoura, Blenheim, Rolleston,
Picton, Levin, Porirua, Hastings,
Paraparamu,  Peekakariki,
Dannevirk, Palmerston...

You get the point.

An aside: Actually, there is a New Zealand version of the song, by John Grennel, done in the sixties. Easiest job ever, considering Kiwi place names. The Maori called this country is Aotearoa, which I think means something like 'no consonant shall be vowel-less'.   

Sure, it'd be great to fly sometimes. And god knows, in other countries (I'm looking to you, Laos) the bus can be downright brutal. But compared to the alternatives, and for ease, price and convenience, the bus system in this country is pretty darn good. And the traffic, winding roads, and unpredictable weather are someone else's problem.
Here's how I'd break it down:
If you're a young couple, a group, or retired; are staying over three months, and wandering the whole time; have a maintenance/insurance budget; and don't have to worry about tying up your money, then by all means buy a car.
If you're staying for just a month, and want to travel a lot, have a family, and want to economize on hotels, rent a camper van. Remember though, going between the islands will cost you.
If you're travelling alone or are on a budget, even if you're staying an extended period, take the bus.
If you're staying at particular places for significant length of time (as we were, house-sitting), then rent a car short-term if you have to. Otherwise, take the bus.
In the end, we were quite luckily, and our wonderful house-owners in Whangarei lent us their beater truck. We got to travel the North Island's northern peninsula pretty thoroughly, at our own speed and pace. Best of both worlds.