South Island is more scenic on all coasts, but if you want a more diverse then the West Coast of the South Island great.
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1: Pancake Rocks
2: Fox or Franz Josef Glaciers
3: Lake Matherson
4: Haast Pass
5: Arthur's Pass
6: Queenstown
Some of the places I would recommend you to visit. If you self drive I would if you have the time, fly into Christchurch, rent a car, drive north to Blenheim, with stops at Kiakoura to where you can see seals, and they have whale sighting trips there.
When at Blenheim, visit some wineries, then you can travel to Picton and see the Marlborough Sounds, travel over to Nelson, goto Farewell Spit, travel down to Wesport via the Upper and Lower Buller Gorge Roads, then travel to the West Coast from Wesport by the Coast Road, via Charleston, then Greymouth, with stops at the Pancake Rocks etc ...
The rest is upto your imagination.