How did you choose these three unis? Do they have a good reputation for the courses you want to do?
Can't help you RE melbourne, but Sydney Uni and NSW both have good reputations. For a choice I would research which one has a better name for the classes you want to do. I would look at course (in the course section
here - the entrance score should give you an understanding of how popular the course is.
For computer science, I think NSW would be better than Sydney.
Sydney, however, is (or at least is very close to being) Australia's oldest Uni, so it has quite a good history, if that is important/relevant.
Also, Sydney Uni is quite close to the city, whereas NSW is closer to the beach (if you are interested in geography)...
I didn't go to either school, I went to UTS, and I was part time, which has a good technical rep. I had friends at both - nobody complained about the social life
