It's a tough choice, and they don't provide much information because most local students just choose based on proximity. No one schools is significantly better than the others, although some are known for certain specialties. Here's my impression after about 6 months in the program:
Central (RPAH) -
Pros - most international students come here because it's the closest to campus. Proximity is nice; you can get involved in long-term research projects (since you can just walk there during the 4 days/week when you're not at the clinical school during your first two years), go to seminars (although anybody can really go to those seminars), etc.
Cons - RPA doctors are said to be the busiest, so they are notorious for being relatively unavailable to help students outside of their scheduled tutorials. Since you're already on campus 4 days a week, it's not uncommon that they'll reschedule at the last minute and tell you to come back another day. Of course, that doesn't happen often.
Northern (RNSH) -
Pros - I chose Northern as my first priority primarily because they have the most options for clinical rotations/electives. The number of options was the only way that I could seem to quantitatively distinguish between the schools, so that's how I made my decision. They're also known to have a relatively strong radiology department, which is a field that I'm very interested in. The entire hospital is currently being rebuilt, so you'll do at least one of your clinical years in a brand new facility (it looks very impressive if you check out their website).
Cons - If you go to Northern, you're not guaranteed to get into Royal North Shore Hospital. Some of the Northern students are shipped off to Manly and Hornsby, which are smaller hospitals (so you get more personal attention, but you have fewer options/opportunities).
Concord
Concord is the best of both worlds. You sacrifice proximity (which you get from Central), but you don't have to worry about professors being unavailable. You don't have a large number of elective options (like you do at Northern), but you also don't have to worry about being sent off to Manly or Hornsby (although Manly is right on the beach, so it's not that bad).
Westmeade
Pros - It's a good hospital in a good area, and they're particularly known for Westmeade Children's Hospital. If you're interested in pediatrics, you should definitely go to Westmeade. I think they also have a couple of other good programs that you should check out, but I'm not sure about the details. Other than that, I can't think of any good reason to go there.
Cons - It's physically farther away, but there's an express train that goes to that area from campus. If you catch the express train, then it doesn't take too long to get there. Also, some people say that the West Sydney area is "unsafe", but I think it's still safer than most cities in the US.
Nepean
Pros - Real estate in that area is cheap. Nepean students will go on forever about how great their school is, but I've never heard any concrete reason why it might be better. I get the suspicion that it's just where they send most of the people who couldn't get into their priority clinical schools, and some of the people who have bonded places.
Cons - It's all the way out in the boonies. If you take the train, I think it takes over 90 minutes to get there from the city (don't quote me).
Did I miss anything?