Not to contradict gazzaputt, just a preference for hills (which you will encounter one way or the other) and greenery and a wariness of the motorized denizens of Bromley and Catford, but I would cut across country to West Wickham via Blackness Lane, Jackass Lane, Gates Green Road and Glebe Way and then on to Crystal Palace (via Anerley Hill, ahem), Dulwich, Camberwell etc. The only regular encounter with numpties I have is around the Elmers End roundabout which should be crawling if you're commuting at normal times.