Both are equally good. I know some UK students who left to study medicine in Australia, and some Australia students who came to study medicine in the UK (in the later case, the UK gives some full scholarships to the Aust/NZ students to study med in UK, but they were as hard to get as a Mitchell scholarship, like only 5 students or so--one was benchmarked for Trinity med in Ireland).
Cost of living is siginificanly lower in Australia, which plays a heavy part since you will also have to pay a full tuition.
Your best bet is to somehow work it out such that that you can study half of each year in UK, and the other half in Australia, so you can have a summer year round 🙂