Priorities (in order);
If you have less than a month in New Zealand, spend it all in the South Island.
Try to avoid;
Here's an (unfinished) indexed review of rides published in various books:
Top Escaping Auckland Airport See New Zealand by Bike by Bruce Ringer. Routes; into the city, to motorcamps, and going south. Alternatively jump on a shuttle into town - it's just a 20km ride through busy city suburbs roads. Not much fun. Top Auckland Day Rides See New Zealand by Bike by Bruce Ringer. Three day rides; 50 km loop, Waitakere Ranges, Waiheke Island. Top Northland See New Zealand by Bike by Bruce Ringer. 12 days, 1010-1069 km Route; Auckland-Warkworth, -Whangaarei, -Russell via Kawakawa or Helena Bay, -Whangaroa, -Pukenui/Houhora, -Cape Reinga, -Kaitaia, -Rawene direct or via Broadwood, -Trounson Kauri Park, -Pahi, -Helensville, -Auckland. Top Coromandel Peninsula See New Zealand by Bike by Bruce Ringer. 7-9 days, 466-897 km Route; Auckland-Thames, -Coromandel, plus North Coromandel Loop option, -Whitianga, -Whangamata, -Te Aroha, -Kaiaua, -Auckland. Plus Whangamata-Tauranga, -Whakatane. Plus Tauranga-Rotorua via Ngawero or via Te Puke. Top Auckland to Wellington via Wanganui See New Zealand by Bike by Bruce Ringer. 6-9 days, 604-761 kms Route; Auckland- Kaiaua, -Cambridge, -Lake Waipapa, -Tokaanu, -Raetihi/Pipiriki, -Wanganui via the Whanaganui River or via Mangwhero River, -Levin or Palmerston North, -Wellington. Top Auckland to Wellington via East Cape See New Zealand by Bike by Bruce Ringer. 10-16 days, 1191-1528 km Route; Auckland-Kaiaua, -Te Aroha, -Rotorua, plus Lake Tarawera option, -Whakatane, -Opape, -Te Kaha, -Opape, -Te Kaha, -Te Araroa, -Tokomaru Bay, -Gisbourne, -Wairoa, -Napier, plus Hawkes Bay options, -Dannevirke, -Masterton, -Wellington. Option Rotorua-Taupo, -Tokaanu. Top Wellington See New Zealand by Bike by Bruce Ringer. Intro to/info on Wellington, plus three day rides; Island Bay, Makara, and Rimutaka Circuit. Top Wellington to Auckland via The King Country See New Zealand by Bike by Bruce Ringer. 8-10 days, 731-819 km Route; Wellington-Palmerston North, -Wanganui, -Hawera, -New Plymouth via Stratford or via Opunake, -Awakino, -Waitomo Caves via Te Kuiti or via Makakopa, -Huntly or Hamilton, -Auckland. Top Picton to Christchurch See New Zealand by Bike by Bruce Ringer. 3-5 days, 346 km Route; Picton-Seddon, -Kaikoura, -Cheviot, -Christchurch. Top Christchurch See New Zealand by Bike by Bruce Ringer. Intro and info on CHristchurch, plus two day trips; Northern Summit Road, and Summit Road and Lyttleton. Also a three day ride; Christchurch-Akaroa, -Diamond Harbour, -Christchurch. Top Southern Alps Circuit See New Zealand by Bike by Bruce Ringer. 7-8 days, 573-736 km Routes; Christhcurch-Lake Coleridge, -Arthurs Pass, -Moana, -Reefton, - Maruia Springs, -Hanmer Spring, -Rangiora, -Alforn Forest. Option; Christhcurch-Springfield, -Arthurs Pass. Option; Arthurs Pass-Greymouth, -Reefton. Top Christchurch to Queenstown See New Zealand by Bike by Bruce Ringer. 6-9 days, 484-634 km Route; Christchurch-Rakaia Gorge/Alfond Forest, -Geraldine, -Lake Tekapo, -Omarama, Mount Cook side trip, -Cromwell, Arrowtown/Queenstown. Option; Omarama-Wanaka, -Arrowtown/Queenstown. Top Otago and Southland See New Zealand by Bike by Bruce Ringer. 10-15 days, 747-1155 km Route; Queenstown-Mavora Lakes, -Te Anau/Manapouri, or Queenstown-Kingston, -Te Anau/Manapouri, Milford Sound side trip, -Tuatapere, -Invercargill, -Curio Bay, -Pounawea, -Lake Waihola, -Dunedin, Otago Peninsula side trip, -Middle March, -Naseby, -Alexandra, -Queenstown or Wanaka or Hawea. Option; Dunedin-Lawrence, -Alexandra. Top The West Coast and Nelson See New Zealand by Bike by Bruce Ringer. 10-12 days, 837-908 km or 15-16 days, 1,222+ km Routes; Wanaka-Makarora, -Okuru/Lake Moeraki, -Okuru or Lake Moraki, -Fox Glacier, -The Forks or Okarito, -Ross, -Greymouth or Rapahoe, -Charleston or Westport. Westport options; Cape Foulwind, Denniston, Karamea. Westport-Murchison, -St. Arnaud, -Nelson or Picton via Spring Creek. Nelson-Havelock, -Picton via Queen Charlotte Drive. Nelson options; -Takaka, Collingwood.