I spent a lot of time in London as a kid (dad's family was London based,) and I now like in Sheffield. I think London can be an amazing, vibrant place if you are in a good mood, but as soon as you feel a little down the negatives of the place can tear you apart. Although the price of beer has been the main measure of cost its worth pointing out that my girlfriend and I spend the same on a 2 bed flat with a view of the Peak as a friend does for a single room in a shared house on a major trunk road.
London is also a big place and different places feel different to live in. When my dad was in Wandsworth i much prefered being in London than when he lived in Tulse hill.
As for the friendly people thing my experience has always been its not a reflection of the place but of you. If I sit on a bus in Sheffield not making eye contact with anyone for fear of being asked what I'm looking at then i wont get spoken to, but if I chat to the people around me about the weather I'll probably think "what friendly people".
As a climber the variety available from being based in Sheffield makes it what it is. Having only had a look at southern sand stone on a wet day it doesn't look that bad, but I'm not going to give up being able to walk to Stanage.