First a few clarifying questions: where in Aus are you located? What's your eventual career goal?
If you're wanting an apprenticeship in the airlines, you've got pretty much two possibilities: Qantas Sydney and Qantas Brisbane. If you don't live in either of those cities, you'll need to be prepared to move as Qantas is pretty much the only commercial operator offering apprenticeships.
Which ever way you go, GA or airlines, once qualified as an AME, you're qualified to work on anything from a Cessna 150 to an Airbus A380. It may be a bit more difficult to get a job in the airlines if all your experience is on piston-engined, single-prop bug smashers, but you'll likely find that a good attitude is just as important, if not more so, than which aircraft you did your apprenticeship on.
Given the continuing downward trend of maintenance in the airlines, I'd suggest getting with a GA operator if you know of any taking on apprentices. That being said, apprenticeships in GA are almost rarer than in the airlines. If you're not able or willing to relocate and aren't in either Sydney or Brisbane (or Tamworth), GA is really about your only option.
Whatever path you choose, as soon as you've completed your Cert IV, enroll in and complete the Diploma ASAP as that's your ticket to getting licensed and makes you a LOT more employable, in both the airline and GA worlds.
Best of luck and keep in touch.
Cheers,
John