The most beautiful tracks?

Hi Phil, 30 days doesnt leave much time to play with, alas. Regarding Stewart Island, seeing as time is so short do not do the Rakiura. It is very unscenic and would be a waste of 3 days. You won't have the time to do the full North West Circuit so I would recommend catching the watertaxi to Freshwater landing and walking across to Mason Bay and spending 1 or 2 nights there going Kiwi spotting. Mason Bay is gorgeous. If you have a spare 2-3 hours at Freshwater climb Rocky Mount for some great views over the interier of Stewart Island and Paterson Inlet. Back at Oban spend a day visiting Ulva Island to experience what the New Zealand bush used to be like before humans arived. The Dusky takes 8 days to walk if you do the full thing. A popular cut down version of it is to fly into Dusky Sound and walk out to Manapori taking 4 days, but IMO you miss out on the most scenic part which is the Pleasant Range between Loch Maree and Lake Roe. Lake Roe is stunning and the highlight of the trip. If you dont have time to do the whole thing I would suggest starting at the Hauroko end and walking to Dusky Sound and flying out from there, for 4 days. Whatever you plan for the Dusky though bare in mind that the Seaforth River is a major flood route and any rain experienced while on the Dusky has the potential to cause the Seaforth to flood and make the track impassible. I saw first hand that river rise (and lower) a couple of metres in the space of 24 hours.

Oh I should probably suggest some other tracks seeing as thats what you asked :-) The Routeburn is stunning, and the Milford is supposed to be as well if you can stand the crowds. Might not be too crowded if you come after Easter when the Great Walks season has finished. In the Queenstown area the Rees/Dart is popular and very scenic. Near Wanaka the West Matukituki valley is amazing as is the Gillespie Pass Circuit. All of these tracks are in the 3-4 day length timeframe so doable if you are in the area.

Also you could try the Kepler great mountain views

Kepler, Rees Dart, Routeburn, Queen Charlotte. Cheers.