Mainly class size, location and flexibility to complete some electives in North America. As for the PR question it varies based on your situation but ultimately not too difficult. Some rural areas will sponsor you for PR while alternatively you can apply after a certain amount of time working based on the visa you are on
All medical schools teach essnetially the same cirriculum to be honest. I think location and cost will be your biggest decision making factors. There is some more perceived 'prestige' with coming from a more established and older medical school (e.g. University of Sydney), but to be honest, when most Australian hospitals and clinics are hiring & interviewing, they don't care which University you went to, so long as you're safe & competent, prepared to work hard, and got a good personality & attitude.
PR is a separate issue. After graduation, once you're employed & sponsored by your employer, and after staying & working in Australian for a certain length of time, and after passing a bunch of assessments (e.g. English language competency, Australian history, criminal history checks, referee checks, etc.), you may apply for permanent residency or citizenship. More information on the Dept of Home Affairs website.