Like many here, I like Lockwood's proposal. The use of the colors of the Union Jack is a sufficient nod to New Zealand's European history.
I'd rather they keep their current flag, but if they must insist on changing it, this would definitely be my top choice, especially if the
Tino Rangatiratanga doesn't get more appeal beyond the Maori.
As far as Australia goes, the problem they have is that most of their alternatives are awful, enough to make their current flag look beautiful by comparison.
This is quite possibly the only one that actually looks half-way decent: