From what you've said, I would suggest looking more into the Leeds course. You're obviously not going to be 100% happy with St Andrews, and although you may love it when you arrive, I wouldn't take the risk. Is there an open day coming up that you could possibly attend? If the nightlife is what you care more about, then it may be more for you.
However, if you are interested in a course that ranks between the two, you may be better off taking a gap year, to assess your priorities and apply to different universities. You could use the year to gain work experience, travel and try new things. Considering St Andrews has accepted you, you must be quite intelligent, so there may be universities out there that give you the best of both worlds.
A third option would be to contact your other universities. I'm not sure whether or not they offer neuroscience, but if they do, they may be willing to switch you onto that course, in which case I would call them up as soon as possible. As they are all biological-science related, it would most likely be within the same department- it's not as if you're asking to go from Russian to neuroscience!
Anyway, I can't think of anything else to add, so all the best, and good luck regardless of what course you choose to do! xx