Dwarf Cavendish - Needs warmer conditions than the lady finger types.  Also a great option for the green house.  Small plant growing to around 1.5-2m but still capable of producing large bunches of fruit, similar to your supermarket type banana.
 
Growing bananas in NZ
Bananas grow great in Northern parts of NZ, particularly the lady finger varieties.  They thrive in warm, sheltered conditions and require plenty of compost, mulch and water.  They are considered heavy feeders, the more you feed and look after your bananas the more fruit you will get.  Bananas will form a clump in no time and it is important to keep on top of the clump to ensure good fruiting.  Ideally you want to keep your clump to 3-5 main stems.  Any extras can be removed and mulched back around the clump.  Although typically grown in the northen parts of NZ, we have customers who have created micro climates to successfully fruit bananas outdoors as far south as Christchurch.