Not sure on the specifics for comm/law... but in general usyd and unsw are both great uni's so don't worry too much about one giving you a bad education.
In terms of exams, most usyd exams are handwritten, though it depends on the subject. I know at least some law exams are open book... don't know how common that is though since i don't study law.
In terms of clubs and societies, no employer is going to give someone a job just bc they joined a society. It might look good if you were an exec or something but there are lots of ways to get that leadership experience. Don't know how they compare, but both usyd and unsw have plenty of clubs across a range of areas. Good to join once you are there but not needed. If you are really worried about employability then focus more on getting internships or working for academics later on.
last thing, don't discount which uni you like more. Doesn't have to be a specific reason... but you want to enjoy being at uni. I do think that you will be able to enjoy both fine once you are there... but if for some reason you just want to go to a particular uni, that could be the deciding factor.
Don't stress too much... try to get an offer for each across the offer rounds if possible and give yourself more time to consider. You have two great options... do your best to determine which is best for you but remember that you are not risking choosing a "bad" uni/course. Also, like always, transferring is an option.
