Hi,
The computer allocation system basically takes into account all of your preferences (single or mixed sex apartment etc, which hall you would most like to be in), also gives you a priority level (so you are given a lower priority if you live within the M25) and tries to match it to a space in halls. So if you put Stamford Street down as your first choice, it will try and find a space there which matches your preferences. If it can't find one there, then it will try in your second-preference hall etc. etc.
I personally think the halls are very nice... I lived here for two years as a
King's student (my first and third years) and really enjoyed myself. I was really impressed when I first came down to London (back in 99) because the only other halls that I'd seen were my brother's dilapidated ones in Leeds. It's definitely an advantage having your own bathroom, it's really good to have your own fridge as well....the only downside that I could see as a student was that the rooms aren't huge... but definitely big enough to live in comfortably.
Waterloo is a fantastic place to live, it's really come up a lot in the last 5 years. There's loads of bars, pubs and restaurants around, it's really close to get into college and town, and the river is the best thing in London.
Hope that helps,
Tom Elphick