If you are looking for parties and the American experience, do consider price. Tuition, room, and board at American universities can be extremely expensive relative to costs of attendance in the rest of the world. Some states' university systems are much less expensive than others, and private schools' prices vary a lot too. Most states have a "flagship" state university or two (in California, UCLA and Berkeley), and most of those schools would suit your purposes pretty well, but you might be expected to work harder than you want to at most of them. I think you would find what you are looking for at lot of less-well-known state schools, and those tend to be less expensive. For example, Towson University in Maryland, George Mason University in Virginia (actually Virginia's largest school), and West Chester University in Pennsylvania probably have what you want. All of them are in the suburbs in major urban areas. I think the Florida state schools and those in the deep south (Alabama, Mississippi, and Louisiana) would have both the climate and the party atmosphere that you want. California is a lot of fun, but expect universities there to be expensive and public transportation there to be limited (relative to the situation in the East Coast megalopolis).
I am not sure that anyone has said this yet, but Americans I know who have gone to Australia for a semester have gone there to party because, in their experience, Australian schools are less academically demanding than comparably regarded American schools. The moral of the story is, even if you go to a good university in Australia, you might find fairly prestigious American schools like UCLA and USC to be the opposite of a big party, given your expectations.
I am not sure that anyone has said this yet, but Americans I know who have gone to Australia for a semester have gone there to party because, in their experience, Australian schools are less academically demanding than comparably regarded American schools. The moral of the story is, even if you go to a good university in Australia, you might find fairly prestigious American schools like UCLA and USC to be the opposite of a big party, given your expectations.