I'm living with friends in my first year at uni, rather than in halls, and I have to say, it has made things somewhat more difficult to make friends, just because I don't go home to fellow uni students, but I've still made very good friends with people on my course. I think it all really depends on your personality; if you said you're not overly social, then you might feel lonely/isolated anyway in halls. I know I would have. I'm very glad that I chose to live where I did, despite the fact that there are minor disadvantages at times.
The main reason I am leaving my current city which has a good Uni to a different Uni is because of the halls experience(I am willing to do whether i get accepted),there are like so many things you can do .Meet new people especially if your in London cause it'll be a Multi-cultural Community and you can learn about new cultures etc.
Friends are made at a large extent and it's way fun when you have a group of friends playing FIFA together in your/friend's room lol. Great Experience which shouldn't be missed out.
You can easily apply for new social clubs/sports/Football team...
To my view it looks as though it never gets boring living in halls.
When living inside the university in Halls you can access to buildings easily just by walking distance,no transport expenses,like you could get to Libraries/Nightclubs/Cafe's/Institute Centres etc etc.
Living with a friend is an opportunity that almost always comes by. You can live with him next year or whenever your ready. So yeah the choice is yours.
Obviously I say Halls