I have done this region both ways.
I sailed it with Holland America, Auckland to Sydney, calling at the regular cruise ports down both New Zealand islands, including the Bay of Islands and Fiordland, then crossing the Tasman and stopping in Melbourne before finishing in Sydney. I have also driven both islands, and I visit family in Brisbane and my partner's family in Auckland often enough that neither country is a place I read about.
That combination is the reason I can answer the question people actually need answered. Not whether to cruise Australia and New Zealand. Which parts of it are better by ship, and which parts a ship will cost you.
What the ship does better than anything else
Fiordland is the case that closes itself.
You can drive to Milford Sound. People do, and it is a long day on a road that deserves your attention. What you cannot do from land is sit on deck while the ship moves through the sounds at water level for hours, with the walls rising on both sides and no schedule to keep. The scale of that place is something you understand from the water in a way you do not from a parking lot at the end of a road. A ship gets you there without the drive, without the accommodation problem in a region that has very little of it, and without the weather gamble of a single booked day.
The Bay of Islands is the second one. Arriving by tender is a good way to see it, and the logistics from land are more effort than most itineraries can spare.
Then there is the obvious structural advantage. Auckland to Sydney is two countries, a great deal of coastline and an ocean crossing, and you unpack once. For a first visit to this part of the world, that is not a small thing.
What you give up, and it is real
New Zealand's interior.
The cruise ports are coastal by definition. What sits inland is a large share of what makes the country extraordinary, and no ship reaches it. Driving the South Island is one of the great road trips anywhere and a ship does not replace it. If your picture of New Zealand is the alpine landscape between Queenstown and the West Coast, a cruise will show you a coastline instead.
The same problem applies in Australia in a different form. Melbourne is a good port call and a poor way to see Melbourne, because that city rewards days rather than hours. One port day is an introduction and nothing more.
The Tasman crossing, which nobody warns you about
Mine was rough.
The Tasman Sea has a reputation among people who have crossed it and almost no profile among people booking their first sailing here. It sits between two land masses in the path of a persistent weather system, and it can be uncomfortable for a day or two.
This is not a reason to avoid the itinerary. It is a reason to book a mid-ship cabin on a lower deck if you are at all prone to motion, to have something on hand before you need it rather than after, and to know it is coming so it reads as normal rather than alarming. I would rather you hear this from me now than work it out at two in the morning in the middle of the Tasman.
How I would actually plan it
For most people the answer is not one or the other.
It is the sailing for the coastline, Fiordland and the crossing, with land time attached to one end. Add days in Sydney or Melbourne after you disembark, or a South Island drive before you board. The ship handles the part that is better by ship, and you keep the part that is better by car.
That is a more complicated booking than picking a cruise off a page, which is exactly why it is worth having someone build it. Flights from North America into this region are long and the routing matters more than the fare. The cruise line's own pre and post packages are rarely the strongest version of the land portion. And the seasons run opposite to yours, which catches more people out than you would expect.
I am Australian-born. My partner is a New Zealander. I have sailed this coast and driven these islands.
Ask me the awkward questions before you book. That is what I am here for.
Planning from the United States? See how I plan Australia trips for American travelers →