I went to UTS for a year and I'm now studying at UNSW so I can give you a bit of an insight into both Unis
UTS- as a first year I found UTS to be quite welcoming. I studied Communications/Law btw. The people were really nice and down to earth! Definitely didn't feel like it was cliquey at all. UTS also had awesome food seeing as Chinatown was literally right outside- never ending choices. Only downside- because of the sprawling nature of the campus, it definitely lacked the 'campus' vibe of UNSW which I really love. It's also not as big in terms of clubs.
UNSW- for me, I really enjoy UNSW because of its social vibe. The people I've met here have been equally down to earth, very welcoming and inclusive. I don't know if it's just the people I've happened to meet, but seemingly across faculties (I'm doing Arts/Law), I've found that people are extremely nice. Again, not a cliquey Uni, but I've heard that within Comm it can get a bit cliquey just because a lot of people attended the same high schools. I haven't found this to be the case in Law or Arts, so can't really comment. Food at UNSW is pretty good, obviously not as much choice as UTS but there is quite a bit of variety. One major thing I've felt is that at UNSW people are more inclined to chill/ have lunch etc, whereas UTS for me, most people were more keen to get home (me included haha). Downside at UNSW- haven't experienced anything thus far.. perhaps the extra travel (but that's not really a social thing!)
Good luck with whichever Uni you end up attending