The short answer is: it depends.
"Better" is a very, very vague and broad word that cannot encompass everything. There are lots of factors to consider - employment prospects, reputation, degree structure, subject choice, technology and resources, campus quality, friendliness/student character, eateries, convenience, administration, lecture hall/room/lab quality, staff, social activities, clubs & societies, expenses, aesthetics - the list is extensive.
Additionally, while some information on the characteristics of univeristies is useful, I wouldn't place too much reliance on the commentary by most people here when comparing the two universities directly. Generally the only thing that you should take into account from the posts is how happy they are with their course at their particular uni. (People can vouch for their own experiences at their own uni, but typically they cannot say that theirs is better or worse than another with any true accuracy, not having experienced it for themselves).
I have attended both UNSW and USYD, so if you have any specific uni questions, then feel free to ask. However, asking "which one is better" is just too vague and subjective. Discussing "what are the good and bad qualities of the respective universities" might be beneficial, especially if each poster states which uni they are attending.
[lol @ NTB]