Another element to consider: you’re coming from Australia.
Do you want something a little similar to Australian structures of higher education, something that feels similar? Then choose UCLA (I think it’s a good equivalent to UMelbourne).
Do you want something uniquely American and unlike anything you’ve experienced before? Then choose Vassar (there’s literally nothing like it in Australia).
As for the cold: you get used to it. You wear a coat, earmuffs, mittens. You get to tell tales to your family and you impress them JUST FOR WALKING OUTSIDE!! 
I came from a town where I could wear tee shirts in October, and went to college where there were 4-5 months of snow and sub zero temperatures for a while. It *really wasn’t so bad, and it actually was kind of fun to realize my sense of temperatures changed, also to do all the things you can practice in the snow, from snow angels to tray-sledding to broomball, not to mention snowshoes, snowmobiles, and even sleighs, either with dogs or with little bells (yeah, those last two are for tourists and I got to do that as a holiday treat, but it was fun nevertheless). In short, don’t choose based on weather.
Another thing: most college students’ life centers the college. They may go into the city a few times a semester, but what matters is what’s going on on campus. Both colleges will provide you with tons and tons of things to do. You’ll be busy 24/7 and if you’re bored, it’s because you’re trying very hard to!
- Don't buy them in Australia. Buy your winter gear on location, where they'll have plenty of clothes that'll protect you from low temperatures. :)