Prestige of degree v Quality of education. Those are probably the two major factors, as well as convenience, etc.
Within Australia (and probably overseas as well), the difference isn't substantial. I remember talking to ninwa about this, except I was also considerign USyd, and essentially once you get into a G08 uni in Melb/Syd it doesn't matter. What does matter:
- your GPA
- Internships/Work Experience
- your co-curriculars
- your extra-curriculars
- how well you interview
- how well dressed you are at the interview

+ some other things I forgot exactly, but you get the general gist..
Honestly the decision should be an easy one - choose the Uni in the state you live in, unless you have a huge desire to go interstate.