The B767 is used on long-distance or peak routes such as MEL - SYD, SYD-PER, MEL-PER. It can be used on the MEL-BNE (I remember it recently) but the volumes on this route clearly show that a B737 is the better choice.
Qantas do not offer B747 service domestically any more (and, just so you know, a B747 is a jumbo, nothing else), the largest aircraft you will be on is either a B767 or an Airbus A330.