We are trying to decide if we should spend all our time in New Zealand 2-3 weeks or should we allow time to visit Australia. Many people have commented if one was to return to that area they would go to New Zealand. We are planning on renting a car.

Any tips on sources for accomodations and car rental would be appreciated.

Two to three weeks is hardly enough time to do justice to NZ - so I'd go there and forget OZ - you wouldn't even start to scratch the surface of Australia if you tried to combine it with NZ in that time frame. Australia is as large as USA and you'd spend a lot of time at airports. We used Apex car rentals in NZ with absolutely no problems, although have read recent complaints on this board.

A friend and I managed a 3-week trip to NZ and OZ. We "did" the north island for a week and then went to Tasmania for 5 days, Cairns for 5 days, and then Sydney for about 4 days. It is do-able, but no, you won't see everything in either country in that amount of time. It depends on what you want to see.

This question has been asked many times before. I would suggest that you search on this site for information about both countries and do some research.
We can't tell you what you will or won't like because we don't know you.

In 1999 I did a three-week trip to Australia, New Zealand, and Fiji. Obviously, you can't see any of these places in depth on such a whirlwind trip, but it gave me a little bit of the flavor of each place and whetted my appetite for more. I have returned to Australia twice since then.

Everyone travels differently, and for some people, a whirlwind trip such as mine would be totally unappealing. But for me it was the right thing to do, and I absolutely loved it.

If you have a desire to go to Australia, even if only for a week, then my recommendation is to follow your instincts. Whichever you choose, have a wonderful trip.

We just spent our honeymoon in Fiji and New Zealand (1 wk Fiji, 2 wks NZ). I think it would be very hard to cover NZ and Australia in the amount of time you're talking about. We limited our time in NZ to the South Island and still missed alot of things we would have liked to see. If you're dead set on doing both, I'd head straight to Queenstown in NZ...the natural wonders there are breathtaking.