It really depends on what majors you are planning to do in your commerce degree and whether you are planning to combine the commerce with either arts, science, social science or law.
If you were planning to combine it, then commerce/law might be a bit better at usyd, as their law degree is a little more recognised. But apart from that, the other combined degrees at unsw are great!
If you were planning to do commerce and do a double major, unsw would undoubtedly be the best, except for the major of actuarial studies, which is more recognised at macquarie university.
At the end of the day, no matter which university you decide to go to, the content is primarily going to be the same, its just the actual experience and recognition in the workplace that differentiates the universities. I love going to unsw because its a fairly large university with excellent facilities, but not to the extent where you feel cut off from your friends outside the commerce faculty, which is why i opted out of usyd. I also love relaxing on the lawns between classes, which is why i opted out of uts.
But the most important thing is actually getting a job out of it of course! i'm in my last year of my degree so i've been exposed quite a bit to the interview and screening processes that the large firms make you go through before taking you on as a graduate. I would have to say that the majority of the people that they interview and give job offers to are unsw graduates. For example, at my PriceWaterhouseCoopers interviews, over 50% of graduates were from unsw, 25% from usyd and the remaining were from the other unis. so i think the numbers speak for itself!
But to provide a more balanced view point, the buses to unsw are at times dodgy and i wonder why they thought building a uni on a bloody hill was a good idea!!!
So goodluck with your decision and i hope you make the right one!