Campus aesthetics - Having attended both universities, the external campus aesthetics at USyd would be my preference. Whether it be enjoying the sun while overlooking the lawn or sitting under an arch in the quadrangle, the environment is very pleasant. Although, it takes forever to get from one side of the uni to the other. Hiking from Wallace to the Economics and Business building is an absolute pain.
Also, USyd interiors are generally old and not very appealing. USyd's Carslaw lecture theatres house some of the most torturous seats ever created by man. I think UNSW really has the edge in terms of interior. We seem to be more up-to-date. But on the outside, USyd is magnificent. (The exception is our new law building, which on the outside completely trumps the USyd 'office-block' design of their new law building.)
Campus food - UNSW has far more places to eat, with much greater diversity, than USyd. The eateries at USyd are both limited and bad.
Social life - UNSW I think is generally friendlier. USyd has social events but you have to put yourself out there and search them out. If you join Subski or some such club with a bunch of friends then you have a good start. But I think at UNSW there are more opportunities all around you. There are plenty of socities at each uni to find people with common interests. One thing is that, because UNSW is more compacted, and more urban, you find you bump into people more than at USyd.
Transport - USyd is convenient to get to from Central - just a quick 10 minute bus ride. UNSW does have dedicated, express buses to uni however, which also makes travel easy.
Student attractiveness - Depends on your taste, because at UNSW, 50% of people are from non-English speaking backgrounds, where as at USyd I think it is something like 35-40%. Generally I think the ratios of attractive people are fairly similar, but in my opinion USyd's Arts students generally can't be beaten on numbers. Especially the Psych girls. On the other hand if you like Asian guys or girls then by sheer numbers UNSW probably has more hot ones. Other than that, both unis are fairly equal.
Timetables - USyd's system is terrible. Highly inflexible because you can pretty much only select times when you aren't available and let the system generate a timetable around that. You have to go all the way in to the student centre to customise it. UNSW you can customise everything - all your classes - exactly the way you want it, all online. It is extremely efficient and convenient. You can also perform many other functions using the UNSW system, like picking up and dropping subjects, etc.
Lecturers - Depends on the faculty, but generally both unis have a mix of good and bad lecturers. Certainly for law at UNSW, I have been fortunate to have had good lectuers. But there were some fine teachers at USyd also. David Braden-Mitchel in the USyd philosophy department is probably the most memorable and entertaining teacher I've had in a long time. It's really a roll of the dice wherever you go. Although, UNSW has a far more advanced timetable system, so you can find out just who is teaching what and specifically choose certain classes with decent teachers.