Arithela said:
Which one is better in terms of quality of teaching and reputation?
It's very diffcult to answer that question because not many students have attended undergraduate study in the same scientific area at both university. Even then it is difficult to tell you whether the quality of teaching in ONE area of science (e.g. chemistry) is consistent with all other areas of science offered by both university.
What area of science are you most interested?
In terms of reputation, both USyd and UNSW are similar, with Usyd being more traditional due to its long history, and UNSW being more modern and vibrant.
Please do come to the Open Days and find out for yourself what the atmosphere is like. I think either one of the universities would be a great choice and will not make a significant difference to your employability - we all learn the same material (most of the time using the same textbook!). It is your individual performance that will make you stand-out when you graduate.