I'm not really in a position to be informative (I'm doing my HSC too), but I'm in the same position as you. From what I've gathered, going to the open days, and what undergrads say on the forums;
UNSW
- More reputable business school
- Less lecture based, focused more upon working in classes and real-life application
USYD
- Generally more prestigious university
- USYD's combined law program is more superior
I'm leaning towards UNSW, but I think it doesn't really matter, so long as you get good marks, ec's, etc.
Also consider ATAR requirements. UNSW is probably easier to get into (96.3 can be reduced to 91.3, with bonus points in Eng Adv, Mathematics and higher levels, which you would probably be doing if you're looking at an atar in the mid 90's) as compared to USYD (95 without any bonus points, apart from EAS etc).