Big decision to make. Very daunting possibly most important of your life.
There are various resources to aid your decision making. Friends and fellow students. Current interns. AMSA IRG.
Although it is pretty much a lottery you will impress people if you make contact with the JMO Managers at the individul sites and ask for some information about available terms, Consultants you can talk to about career paths etc...
Let me put in a plug for the Hunter New England. Very progressive service which excels in the educational needs of JMOs and service improvement. Matched by a more affordable and less crowded lifestyle than Sydney can offer.