Both USyd and UNSW have very good business schools. As such, you cannot go wrong with the Bachelor of Commerce at either university. Essentially, favourable academic performance and gaining work experience during your time at university are the two main elements that will maximise your competitiveness when applying for jobs as a graduate. Of course, the Bachelor of Commerce is a multifaceted degree and choosing between USyd and UNSW involves considering more than just the Bachelor of Commerce as a degree.
First, you should consider the specific field(s) that you might be interested in, as each university may excel in certain areas more than the other. For example, my understanding is that the Human Resource Management major at UNSW is slightly more practical compared to the more theory-focused Industrial Relations and Human Resource Management major at USyd.
Second, opportunities to gain work experiences (such as internships) which universities may facilitate are another factor that can assist you in making a decision. Any relevant experience gained as a student can improve your chances of being selected for a graduate/entry-level role compared to students with little to no experience. UNSW offers a 4-year Bachelor of Commerce (Co-op), which in addition to the standard Bachelor of Commerce, focuses on providing students with work experience thanks to partner employers. USyd may offer similar opportunities, such as through the Dalyell Scholars stream or the Industry Placement Program.
Lastly, while this factor is not directly related to the Bachelor of Commerce, you may wish to consider whether you would prefer the standard semester system at USyd, or the trimester system at UNSW. A semester is longer than a trimester, which could mean less pressure. On the other hand, you can complete up to 9 subjects a year under the trimester system compared to 8 subjects a year under the semester system. This creates the opportunity to graduate a term early.
I hope this helps!