Any car seat that you buy in Australia complies with Australian safety standards, which are far more stringent than anywhere else in the world - so whatever seat you buy is going to be "safe".

Depending on where you shop and who pays for the research, you will get a different response as to what the safest car seat is. I've bought the Turn-a-Tot, which according to some research is the best there is - according to some baby stores (that have been denied distribution rights!) its not safe! Choice recommend it - and that's good enough for me! Its also one of the smaller seats, with more recline positions than the Safe N Sounds, so might be worth checking out for space issues.