I suppose it depends on what your interests are.
I particularly love the outdoors in the day time but would like to explore the city and suburban areas by night or have somehwere comfy to retreat to. For this, Melbourne & Sydney are my favourite. There are awesome day trips particularly for outdoor activities you can go within about 1- 3 hours from the city. There are awesome towns in the surrounds to extend your reach.
Also, you can't really go wrong with Brisbane and the Gold Coast. Great tourist destination with plenty of things to do with a laid back culture. Also if you drive up you can do awesome 4WDing and also if budget permits visit the Whitsunday Islands.