Actually 3 weeks to visit Australia and NZ is a really thin time. I went in Australia last year and I traveled there for 6 weeks. During this time I have been only along easter coast! Yes, I know, I traleled slowly but Australia is sooo big.

Even though I hate tours and love organize my trip by myself, I suggest you to take a tour. If you realli want visit both Austalia and NZ, the risk is rushing too much and lose many interesting place. Better is visit only Australia or NZ this time.

Enjoy, Marco in Milan (Italy)