@jella here are my inputs sa 3 AU city states of comparison as follows:
1.) Sydney - cost of housing is way too high among other states but expect a busy city life a little like comparing it to Makati CBD puro tall buildings and dominated by most white race though meron din daw mix of other races. Transportation is good din naman pero consider having a car din kasi malayo din ang suburb from CBD around an hour drive din. If your profession is IT then you will have more chances to get work. Also, if you would like to study, Sydney is a great hub for schools/universities. If course, popular attractions din like Sydney opera house etc. Marami din beaches dito to visit.
2.) Melbourne - a little taste of Europe ang environment setting though parang mas liberal ang tao dito. Much laid back than Sydney and the weather is much colder. Considered as one of the world's liveable cities in the world. This is also a place for IT professionals mostly and the houses are a bit cheaper compared to Sydney. Of course, if you prefer seeing Formula One race (like me) and World Tennis Cup, nandito yon. I have heard lang marami drunkards sa place kasi nga malamig na lugar and pagsapit ng gabi after coming from work, marami nasa labas parang Malate Manila. The best ang transporation modes dito kasi aside from bus and taxis, meron sila trams at pwede ka mag bike dito safely. Japorms ka din kasi dito ma wewewear mo ang boots mo hehe..
3.) Brisbane - you can experience multiple weather daw in a day. Maaraw, naulan na environment. If you will read, surrounded ito ng maraming lakes. Laid back compared to Sydney and Melbourne at mas peaceful as you're much away from traffic conditions. Marami din ditong Manufacturing plants kaya ok din sa job opportunities.
Hope this info helps a bit.