This is opinion only, since I do not have a moniter, but I am in the same situation as you. I want one
If you want a smaller moniter I would look at Ackies. Paul from BIghhill Reptiles has some I think.
But if I were looking for a larger lizard I think I would lean towards the Tegus.
If you want to see a full grown Black and White, go to "The Reptile Store" in Hamilton. Paul (different guy) has an adult there that is pretty cool.
Good luck in your search.