Yup, plenty of posts on this already.
Colleges - no choice, some way better than others in terms of facilities and condition but the others tend to make up for it in spirit and character. You'll love wherever you end up as always.
Nightlife - If you want to really party hard 7 nights a week in a different club everytime where you don't know anyone except the person you came with, don't come to York. If you are more for a couple of studenty nights a week in clubs where you know all of the students out that night will be, as well as cheesy campus fancy dress events and doing the odd unusual thing like seeing a play or something (DramaSoc plug for you Melana!), York is more for you. You can always go to Leeds if you fancy raving it up a couple of times a term (and spending a fortune!)
I love the atmosphere on nights out here, I have a friend at Leeds who I know would hate it now he's used to going out there.