It’s all relative innit?!?!
If you want to get your PPL in the minimum time available there are ways and means of enhancing your chances.
First, where?
To get up to speed with class C or D procedures and traffic, particularly at busy aerodromes (yes, well aware that not all C and D's are busy, and some OCTA are) will obviously take more time than if you are training at a flying school based within a regional CTAF or Multi-com. More complexity means more hours will mean more $$$ however, will the simplicity of our class G airports put you in good stead for the incredibly cramped airspace of the UK? Dollars saved here could lead to dollars spent there (at roughly double to triple the hourly rate… enjoy!)
Second, what?
What sort of aircraft you learn to fly in could make all the difference in how quickly it takes to earn your PPL. Handling characteristics such as the differences between a C152 and C172 could mean a few hours extra during circuit training. Old beat up training machines would theoretically (and practically) be less reliable and may not always be available when you need to fly during your short stint here.
Third, who?
Who are you doing your training with? If you are going to go for a regional airport due to less traffic, you may have to accept that they will have fewer instructors to dedicate to your needs. If they are already busy, they will have to share their workload with their present students as well as you. I'm not going to even touch on the differences in quality of instructing...
Fourth, when?
Seasonal differences in weather patterns could make quite a difference in how long it takes to get your training done. You might have your heart seat on flying the tropics, but Cairns, Townsville and Darwin all get pretty wet at certain times of the year. Same goes for down south. A bit of research could allow you to enhance the time you have over here.
Other things to investigate before you arrive should include the requirements for converting your licence to the country of your origin, and what you can count as credit (if any) to a PPL in your own country if you are unable to complete the training while here.
Oh, and order some Australian text books NOW and get into the study well before you arrive, it will save time when you get here. Bob Tait writes some great books, and the Aviation Theory Centre have Student Pilot Kits, either of which would make an invaluable investment.
For my money, I’d see if I could get an extra bit of time to ensure that you are getting value for your dollar/pound/euro as well as a PPL, or if time is too restrictive, go for the GFPT and try to get credit back in the UK. Good luck whichever way you go, and enjoy it while you’re down here.