Minai, from most accounts commerce is better at unsw, but arts is more established at sydney. You have a similar dilemma to me with my comm/law.
Also I have also heard that some arts courses (ie if ur more interested in languages, history etc...) are better at unsw or sydney, so look into that.
Either way, both unis are excellent, so you may have to take into other factors, e.g transport (i see u live in chatswood - usyd's straight down the trainline, whereas unsw is difficult by public transport and $6.50 toll each day if u drive, without including petrol and parking). Social lives, extracurricular as well of course shoudl be considered.
It also depends on what ur focus for commerce is. I've heard from several sources that if u want more public sector commerce to go to usyd, the more traditional and theoretical stuff etc.
Unsw is more up with the finance, stockbroking, investment side. Different sources say different things though. *sigh* Good luck with the decision making!