Well, I would say it's a matter of how wealthy you are, if you're rich, Sydney no question!
If you're not very wealthy, I'd probably go with Brisbane, it's a bargain, a great city and the countries 3rd largest city. So it's size means you have good access to quality jobs and universities. It's just an hour from the Gold Coast as well, with a lower cost of living than Sydney, Melbourne and Perth.
Here are the major cities average house prices.