Why do you say 'naturally I want to live closer to London'? Especially having never been there???
My university is in London, but I specifically didn't want to live there, so I'm doing a distance thing and living in Somerset.
I personally love Manchester and find it a much nicer place than London. (If I have a choice of places to work after I get my degree, it would be at one of the unis there.) But there are probably equal numbers of people who like each city. It's personal preference, and it's really going to come down to what you like.
That said, I do agree with hollyberry... If you're coming to the UK for a grad program, go for the program, not its location.
Also, in regards to Brunel, it's not exactly 'in London'. Yes, it's closer than Manchester, but folks I've known who went to Brunel rarely if ever made their way into the city.
When are you planning on starting? Do you have the time/resources to visit the campuses?