Previously this year, I faced your dilemma. UNSW or USyd? USyd had already called, assuring me of a place in their science (medical science)/MBBS program. After some musing and much angsting, UNSW won out for me. These are the reasons why I've chosen UNSW:
1. Less pressure: Think to yourself - what kind of person are you? Be honest to yourself. Do you have a tendency to procrastinate? etc.etc. etc. Personally, I had quite enough of studying after HSC year. If you go to USyd, you'll have to maintain a credit average to pass. If you don't, you won't even be able to progress the medicine stage. Now I know that lots of people think it's kind of ridiculous thinking so pessimistically (everybody manages to ask: "If you can get 99.95, how can you not get credit average?").
Life is unpredictable. You never know what's going to happen. You WILL be facing pressure at USyd, especially when you're fighting for a distinction average to maintain your scholarship. You really do not want to be somebody who panics after receiving a single crap mark (you know, the type of person who sees a credit and thinks "OMFG DEATH"). That was what made HSC suck, it wasn't because the course was hard or anything. It was more the pressure (stupid stuff like getting a lower mark than usual in an english essay and panicking that that would drag down your entire average). At UNSW, that pressure won't be as strong.
2. For me, 6 year vs 7 year thing was quite important. I'm not sure whether that matters so much for you, because you intend to do a dual degree, but that extra year mattered for me in med. After finishing undergraduate, you're looking at long years as an intern and then maybe another 6 years of specialist training. Then there's the years spent waiting for specialist training. In short, you'll probably be 40 when you finally leave the university (uni will literally be another home to you). If you could cut an year, then why not?
3. Starting clinical stuff. In Sydney, you get to the clinical in Year 4, after three years of another degree. In UNSW, you start the clinical straight away (again not sure for your dual degree situation). Do you want to gain more experience earlier? It's really all up to you.
4. Social stuff. You're going to have more of a social life at UNSW. Seriously, if you go to USyd, remember you'll be having all these provisional requirements, like that pesky credit average to maintain. That takes work. Getting a credit probably requires quite a bit of work. Balancing work, friends, uni commitments and studying is going to be difficult.
All in all, it's probably a bit too early to be thinking about such things. Getting into UNSW is just as tough as getting into USyd, because you're dealing with more than just a UAI. You have to scrape a decent UMAT (preferably >180s or above to be on the safe side of the fence) and a decent interview (which is actually easier said than done because there are so many uncontrollable factors like interviewer bias). (The USyd interview is more of a psycho check, seriously... out of 22 people interviewed, 20 people found a place and the main competition is for the science degree instead anyway).
PS. Granted, the money is nice. But if you do 6 years instead, you can earn all that money back by working as an intern (whilst the USyd suckers are completing their final year
).
PPS. Just put whatever uni you want first. You can change it anway lol.
Hope my essay above helped. Good luck*~