Qantas is generally fine (no better than fine though). Things to think about are whether you are going to be inconvenienced by strike action, ensuring you avoid any flights operated by BA like the plague, and whether an additional time and stopover when you are travelling with kids is worth the hassle than flying with just the one stop.
For a $3k saving I would fly Qantas over Air NZ with our kids ... but would make sure that none of the Asian carriers (who all have better service) aren't similarly priced! But then our kids positively like flying and enjoy take-off and landing so the more stops the better for them!