You don't need bio for med, unis in NSW don't have any subject prerequisites, and besides HSC bio isn't that useful for med, from what I've heard. Pick whichever one you're better at.
I have a few questions regarding medicine at UNSW:
1. Should I start preparing for the UCAT right now?
2. What can I start doing that will help me maximise my chances.
3. Does UNSW look at your extra curriculars when you apply?