Essentially, there should not be much difference between the Bachelor of Economics at either university. You can expect to study the same content at UTS or UNSW. Additionally, both universities have good business schools, although UNSW Business School is more well-regarded. However, this will likely not be significant as the university's reputation is not a major consideration here, unlike fields such as law, where attending a better-ranked university is typically advantageous. You can start a successful career as a Bachelor of Economics graduate, whether from UTS or UNSW, and you can maximise your ability to do so by performing well throughout your degree as well as taking advantage of work experience opportunities such as internships during your time at university. Both UTS and UNSW should offer such opportunities, because of which it would be a good idea to contact both universities as they can provide you with relevant and up-to-date information.
Regarding the semester and trimester systems, they each offer different advantages and disadvantages. For instance, a semester is longer than a trimester, although the number of subjects taken under full-time study is 4 in a semester compared to 3 in a trimester. The trimester system can also allow you to graduate a term early because you can complete up to 9 subjects a year under the trimester system compared to 8 subjects a year under the semester system. On the other hand, semesters are not only generally said to be more comfortable than trimesters, but it seems that the trimester system negatively affects holidays in the sense that your holidays would not align with those of students in other universities, which could be problematic to UNSW students with friends in other universities.
In terms of transfers, universities consider your ATAR or your university results, whichever gives you a better chance of admission. For your university results to be considered, UNSW requires you to study at least one year full-time, whereas this requirement for UTS can
vary. Transferring to a different university (external transfer) will require a new application through UAC. If you are transferring to a different degree within the same university (internal transfer), you may not need to apply through UAC, as is the case of UNSW's Internal Program Transfer.
I hope this helps!