The South Island makes for the more scenic road trip. if you are tight on time I'd recommend flying from Auckland to Wellington as your friend did and enjoy the ferry and coastal route through to deviating inland to Queenstown.
As a note: Auckland is not a good place for tourists to get use to the road rules or navigate about. Seriously I found my first visit to the USA driving in LA traffic (in a wide SS Camaro) relaxing in comparison!