As previously mentioned, public transport in London is usually to be avoided by solitary-types. It's not just the people (so, so many people). It's the frantic, frustrated energy of those people that will unsettle introverts and gentle extroverts alike. Everyone acts like they're running late, whether they are or not. The exception to this rule is weekdays on the Overground. Once the morning rush has subsided, the crowds clear out, leaving in their place a few elderly women and sleepy students who will do their best to stay as far away from you as possible. The open nature of Overground carriages makes it easy to wander through the train until you find a seat nowhere near anyone else. If you have a reason to use the orange line on weekdays, then relish the quiet. If not, just start at Highbury & Islington and rock on all the way to West Croydon (and back).