Vipers because rep teams are presumed to have greater depth. I actually think it'd make a lot of sense for you to play for NZ though given the Vipers have Blunder in reserve, so you should talk to AVA about being allowed to swap if you'd rather play for NZ; if he gives you permission I'll roll with it.
If Provincial teams had their own home grounds, then City would surely be unbeatable at home with some crazy spinning deck.