I would go for King's. I'm at KCL now studying English (nearly finished first year) and I LOVE it. The facilities are amazing, the modules are really interesting and the staff are extremely knowledgeable about their chosen areas.
I come from a tiny town in Wiltshire and was scared too about going to London, but it's not scary at all! You honestly get used to it so quickly and I cannot imagine myself living anywhere else.
I have a friend at Exeter studying English and he finds it a little boring there, though the course itself is good.
You can take French for the whole of the first year and I believe in the second and third year as one module. Plus they offer evening language classes with a big discount for KCL students!
There are so many student discounts around London that I don't find money a problem at all.
Safety-wise, I always travel with people and make sure I know how I'm getting home after a night out. As long as you are with at least a couple of other people, the night buses are fine (and are also fairly regular). No one I know has been attacked or anything and I live in the Great Dover Street Apartments, right near Peckham. Security is very high in student accomodation, too (massive security guards, swipe cards, keys, having to show student ID, sign-in and sign-out books, etc). KCL provide everyone at the start of the year with numbers for safe taxi services which I have found really helpful. Some services are very reasonably priced if you and your friends would feel safer getting a taxi home after a night out.
Transport is so so so good in London, too. At home the buses are generally every half an hour (typical countryside!) but on the tube trains are every few minutes, buses are often every 4-12 minutes and taxis are absolutely everywhere.
Hope that helps!