Well big-ish and lots of em – theres a fair few 300m climbs in town so 4 or 5 of them and you’ll start to pech a bit !
Depends what sort of riding you like to do – long rides with views, gnarly DH rides, epics – whatever
My faves (and you might want to pick up the Kennetts booke when you arrive):
Wakamarina which is a bit of a pain logistically – near Blenheim
Kill Devil – Takaka
Queen Charlotte Trk is nice in places and a very lovely couple of days riding.
Will you have transport ? If so opens up a lot of possibilities – Rotorua, Craters in Taupo, Tree Trunk Gge which is highly underrated etc
Anyway get in touch when you are near and I’ll try and show you the sights of Welly at least.