I am a local student at USyd, and I think that you should think about the following points before you make your decision.
I have lived in both Sydney and Brisbane (6 yrs in Syd, 1 yr in Brissie), and it is true that Sydney is a more expensive city to live in, especially the rent. And from what I hear, the international student's fees are 50k/yr in USyd, which I'm assuming is much more expensive than UQ.
Brisbane as a city is much more laid back than Sydney, with less traffic, nicer people, more trees wherever you go. In comparison to Sydney where certain suburbs are associated with certain ethnic groups (eg Ashfield - Chinese, Bankstown - Lebanese, Parramatta - Indian), there are a healthy blend of different ethnicities in most Brisbane suburbs.
Both USyd and UQ campuses have beautiful sandstone architecture and good international recognition, although USyd probably has the upper hand on this one.
As far as the actual med programmes go, they're quite similar, as all the post-grad med courses have been developed in the last 10 yrs and have heavily borrowed elements from each other.
USyd has recently taken onboard the widely held criticisms about post-grad courses (eg not enough didactic teaching of anatomy/physiology etc), and has implementes some changes.
For example, the first 8 weeks used to be an 'introductory block' with PBL topics based on different organ systems (eg cardio, resp, paeds, oncology), but now it'll be 9 weeks with only 4 PBLs and increased didactic teaching sessions. There will also be more practice exams (known as RFAs), and there are also changes made to 3rd/4th yr curricula.
http://www.medfac.usyd.edu.au/currentstudent/usydmp-review.php
Go to the above link and click on the links on the right hand side of the page for the 'USydMP recommendations'.
But these are little improvements here and there rather than a major overhaul, and in the end students with the right attitude will be successful no matter where they go.
Hope this helps, and good luck.