Saw this thread and had to post, hope you haven't already made your decision! I'm a third year physicist at Imperial and hopefully can help you out.
Don't let Imperial's crappy open days and reputation for a poor social life put you off, both are misleading! I went to a similar open day and it was boring as sin, plumped for it anyway as my first choice and haven't regretted it one bit. The social life rumours are largely unfounded.
As a place to live and study for fours years, London is incomparable to anywhere else. It's absolutely huge and full of opportunities, and most of the halls of accommodation are located in some of the most expensive postcodes in the UK, you may never get another chance to live somewhere similar! Believe it or not the first and second year workload become fairly light in the second term, so you'll have plenty of chance to soak it all up. In the unlikely event you get bored, Paris and Brussels are two hours away on the train and halls often organise subsidised trips. You're also far better placed when it comes to your penultimate year and it's time to find an internship, Imperial is targeted by many recruiters and obviously you're already living in central London where most of the big opportunities lie!
The atmosphere at Imperial is very intimate, everyone knows everyone since it's a small college. Yes there's a large proportion of nerds (both male and female), but there are also over 200 clubs and societies to join, all of which are very social, and the social atmosphere in halls is good as well.
If you're going to do Physics here, may I recommend the year abroad option? You can spend your third year in France, Germany, Spain or Italy, and study the language in first and second year (for credit) to get you up to standard. It looks great on your CV and has the advantage of getting you out of second year lab!
Good luck making your choice, think carefully because it's one of the biggest decisions you're going to make! Wherever you go you'll have an excellent 3 or 4 years.