I've never attended either but I have been to both campuses, and know people who have been there.
I think they are very different, UTS is much more of a specialised university, where as UNSW is a more traditional all-round university.
UTS doesn't have a traditional campus either, its more like a really big building and a little grass lawn. There isn't the whole residential system and the whole "mini town" feel you get at the bigger universities like UNSW.
Both are good universities, but as for the "better" university between them, you have to judge the merits of each individual course.