I have advanced certification. But probably going to do day trips anyways cause the trip isn’t based around diving. My wife isn’t a fan of lugging stuff around
You wife lugs stuff around? isn’t that what you’re for? 
Well, it depends. NZ is a relatively temperate country. Not the summer highs of Australia, not the winter lows of say East Coast US.
Most of winter NZ is comfortably above 0C (ie 32F). But that’s different in the mountainous skiing areas in the middle of both islands where obviously it gets cooler.
The upper West Coast of the South Island gets a lot of rain all year around but part of the scenery’s beauty is its bleak desolation.
But if you want to stay warmer but still visit in winter, a warmer place like the Hawke’s Bay is better. Or the far North of the North Island (Bay of Islands etc), that is said to be ‘winterless’.
Charlie,
I think your plan for Australia of the three major locations makes perfect sense.
For NZ, I think Queenstown is the best option for scenery, hiking and wine. It is easy to fly from Sydney or Melbourne to Queenstown. The nearby Central Otago region has many wineries you would enjoy. Take a helicopter trip out to Milford Sound. You might also want to consider driving to Dunedin. We stayed at a very small B&B out on the Otago Peninsula near a penguin sanctuary that was very cool. The only problem with the South Island, as others have mentioned, is the time of year. I’m not sure if it will be too cold at that time.
You are going to have a great time!
Rob
Good suggestions Rob.
Welcome on board to WBs!
Cheers, Howard
I just got back from a (very brief) trip to New Zealand. If you want to have an outdoor/nature focused trip, definitely spend the bulk of your time on the South Island. Due to time contraints, I’m saving that for my next trip there but so badly wanted to do a multi day trek at Abel Tasmin or Milford Sound. Just gorgeous.
Citywise I enjoyed Wellington over Auckland by a large margin. It’s a cool city, and as others have said, a short (albeit slightly daunting) drive to Martinborough (which is very compact, making visits easy).
If you wanted to keep your focus mainly on the South Island, I would get to Auckland a day or two before your flight and take the short ferry ride to Waiheke Island. It’s absolutely beautiful to walk around the vineyard and beaches. Just amazing views. Some nice wine too 
(check out Jurassic Ridge).
Charlie, when last we visited Australia we were there for a month. We spent time in Sydney, Melbourne, Adelaide and Hayman Island. In addition we made day trips to surrounding areas. With the exception of the very end in Hayman and one day at Bondi Beach we did little relaxing. Our itinerary was nonstop moving around. Even after all the time there we still felt like we missed out on so much of the country and even more in the cities we visited. I visited wineries during the day and my wife saw sights sometimes, like Kangaroo Island for example. Sometimes we visited wineries together or did sights together. The idea of adding New Zealand to the mix would have seemed crazy at the time. It would be like going to Texas and New Mexico and then jumping on a plane to New York.
We had good experiences with Qantas FWIW. And Melbourne was our favorite city. My wife has suggested that she would move there if she could. I’m sure you’ll have an awesome time.
I’ve always advised against combining trips to Australia and New Zealand–it’s always struck me that too much time would be taken up in airplanes and airports. Usually folks ignore this counsel, figuring, I guess, that they’ll never head back that way so they’d best see both countries.
Although NZ is far from Australia, it’s really only about 33% more travel time than a flight from Sydney to Adelaide. A lot of the travel time flying is getting to/from airport, check in, waiting for the flight etc. I agree it’s two much for a two week trip but Chaie is going for much longer. I enjoyed Oz a lot but enjoyed NZ more. My trip was two weeks NZ and 9 days Oz. and I wished I had more time in NZ.
Australia is very similar to the U.S., more so than NZ
Prefer not to take two 16 hour+ flights when I can just take one 16 hr flight and one 3 hour flight. For our Asia trips, we usually combine a few countries as well, it’s worked out well. Same as Europe.
Charlie,
With 3 weeks, I think it’s a great idea to do both NZ and Aussie. Sure, you’re not going to get around everywhere in both those countries, but that would take months if not years. The flight between Sydney/Melbourne and New Zealand is 3 hours+, less than many internal flights in Australia.
Now the question will ne what to pick from both countries. With a limited amount of time I usualy advise go to Australia for the cities and NZ for the countryside.
It sounds like you have your heart set on the Great Barrier Reef, so there’s one stop. You may want to consider Port Douglas, which avoids some of the backpacker scene of Cairns.
I would think Sydney is a must. I largely agree with the sentiment that Melbourne may be a better city for my taste, but i think Sydney is a better city for visitors - it’s tends to be just more obvious, Melbourne’s charms and highlights are more subtle. The blue mountains, as mentioned are very easy access from Sydney and are a great option.
You could also do Melbourne, and there really is a lot to commend it. Adelaide is a charming city and does have wine country nearby, although with a limited itinerary I’m not sure i’d head that way. Going somewhere into the country to experience some of Australia’s unique geography would be a good idea, but there are others much better than me to advise where.
For NZ, you may want to seriously consider flying direct from Sydney/Melbourne to Christchurch or Queenstown and circumnavigating the South Island, skipping the North island altogether. The North Island certainly has many highlights, but the biggest drama is in the South.
Some of the top treks have already been mentioned here, and if you;re serious about tracking you should look into the Milford track or the Routeburn, although they book up well in advance.
Two areas not yet discussed in much detail that are musts for me are the top of the South Island (Marlborough Sounds, Abel Tasman, Golden Bay) and the West Coast. The Marlborough Sounds may be my favorite part of New Zealand. Also the Queen Charlotte track is possibly my favorite track. In the middle of summer it’s fairly sparsely populated, in winter you’ll enjoy plenty of solitude. Abel Tasman is also a special track and will be much less crowded at that time. The beautiful beaches won’t be warm enough for swimming. Farewell spit at the end of golden bay would be quite moody in winter.
In terms of wine regions you could do Marlborough (based around Blenheim), Central Otago or Northern Canterbury.
Northern Canterbury is probably the most off the beaten path but there are some very high quality artisan producers in Pegasus Bay, Mountford, Bell Hill and Pyramid Valley.
Marlborough is very much underrated for high quality wine - sure Sauvignon Blanc grows like a weed on the river plains, but there’s some very interesting dirt in the hills and some very committed producers.
I find Central Otago conversely a little over rated. That said it’s a big region and there is no doubt some of NZs best Pinot producers here.
Anyway, let us know what you narrow it down to.
Clayton
i think new zealand is the prettiest and cleanest place i have ever been to. went on 4 days hike on Milford sound track ending at Tasmanian sea…flew into auckland and to hawke’s bay/napier and flew to wellington…rented a car from there to south island/marlborough region for wine tasting and fine dinning. and off to kaikoura to christchurch and off to queenstown
one of best two weeks vacation we took…
Aight. My wife laid down the hammer. She refuses to do more than 7 days in Australia and is only willing to do Sydney and GBR. The other 12+ days will be spent in New Zealand.
In those limited days in the sydney area, where can I go (other than the zoo) to see Kangaroos and koalas. blue Mountain park have em?
For new Zealand, outside of the recs we have so far, we’ve gotten recs for hiking the Glacier, Tongariro Crossing, Kayaking/Rafting in the Fjordlands. She’s given me a day or two for wine in New Zealand, so I’ll have to reach out to some board members for winery recs 
I don’t remember any koalas in the Blue Mountains, but there was one very cool wine shop along the route.
BTW, she can drop the hammer, or lay down the law, but not both She can also lower the boom. I could go on…
Charlie, sounds like fun.
I think you need to work out where you’ll be in NZ doing recreational activities and then fit your two days of wine tasting around that (you could probably do two different wine areas).
In post 31 I set out the main NZ wine districts. Clayton makes a good point that Northern Canterbury has some really interesting wineries where you could easily spend a day. So you should add that to your list of potential areas IMO.
So if you are around Queenstown for hiking, skiiing etc, I’d suggest visiting wineries from the Bannockburn/Cromwell area (eg Felton Road, Mt Difficulty, Carrick, Burn Cottage etc). Or if you were in Auckland for more than a day you could have a great day in Waiheke Island wineries and lunch (and maybe get to Kumeu River). If you’re in Wellington, you could have a great day in Martinborough with recreational activities, lunch and wineries.
When you decide your rough itinerary and timings, I and other Kiwis here on WBs can no doubt give you some suggestions and winemaker contacts for some great visits.
Best, Howard
There are a lot of geothermal sites in Rotorua that we found fascinating. One had boiling mud fields and geysers (geysers are rare in the world). Others had the most colorful (due to magnesium in the water), others were well above the normal boiling point (due to suspended graphite). Almost All the motels have private hot tubs (just stick a pipe in the ground and you have hot water). If this appeals to you, there is a lot to do in Rotorua.
No chance of trading the wife in?
ha. she’s a complicated one to plan trips with.
Cause… now she’s changed our trip destination again. We are going to Switzerland/France/England. Just booked our flights. Can’t beat the deal BA had yesterday on business class flights.
I thought you were a Coche and coach guy.
Did you get the AARP discount? If not, spend a little more time on the travel blogs.
That was a sudden change. haha
what was the deal? (Paid? or miles?)