Thanks for your replies, i'll be renting, not buying.
When i say some of south london is a bit grim, i was talking more from experience of cycling around pekham, parts of brixton, elephant and castle etc. Never felt unsafe, but quite a contrast to places around west london, regents park etc.
Really like cycling around crystal palace and in Kent. I'm staying in Battersea right now - trying to decide on a permanent spot. Most people i know are north/east so thats my preference as long as there is some good spots to do some training.
In terms of accessibility to country roads/hills in North/East, what are some good areas? How about places like Stoke Newington, Holloway, Islington, Whitechapel?