Now, with Medicine the course should come before all other things.
E.g. is it PBL? Do you have ward access from day 1 etc etc etc.
Now, that aside, I <3 Manchester, and of the people I know on the Med course, all are hot girls. However, I know Southampton is another great Medicine course.
Manchester and Leeds have a good nightlife and I can't speak of the others.
But please don't base it on being a good student town! Where there is alcohol and ladies, there is fun.
FYI, I would chose Manchester, Southhampton and Newcastle (not in order).