Two weeks is really only enough to do one of two options, fly/drive between the main stops or do one island properly. The first option will get really expensive, and you’ll spend most of your time travelling not actually seeing or exploring much at all. I would hire a caravan and tour around one island, most people say the South Island is the best one to choose if you only have time for one. I would fly into Queenstown, then go up the South Island. Then if you have enough time you could fly from the top of the South Island/Wellington to Auckland and fly out of Auckland. The spots to visit in Nz are really spaced out, like a full days drive apart most of the time, and flying city to city is not cheap. I would highly recommend campervan, you can stop where you like take it as it comes and it’s way cheaper than hotels and flying everywhere

I know its tempting to do both islands but I would focus on one and do it properly. NZ looks small but it takes more time than you would expect to travel around, of you do both islands over a fortnight you will be constantly travelling. If you like nature go for South Island, if you want nature mixed with cities go for North.

The roads are pretty tame, in south island and the remote parts of North island you can go for hours without seeing another car so I would seriously consider driving.

I would say rent a car or camper van. Driving is not difficult in NZ as long as you are well rested!

I did both islands in 2014 but it was a pretty tough schedule. Auckland -Rotorua- Wellington -able Tasman national park . Then flight to Queenstown to pick up rental car again. Te Anau and overnight in doubtful sound and day trip in Milford sound.

Do not miss out on the sounds if you love nature -both are stunning but Doubtful is a bit less accessible and therefore less crowded. I have been back several times since and would suggest Dunedin area -akaroa near Christchurch , hanmer springs and kaikora in the south and bay of islands on the north island. You won’t fit all in but it does not matter -everywhere is stunning!

Look up Active Adventures. I did the South Island with them, but had a friend who went on and did the North island with them right after. HIGHLY recommend! It was a small group, fantastic lodging, fun active activities (hiking, cycling, kayaking, backpacking, etc). I went on the Kia tour.