For any longer flight I will usually check flightaware for the last couple of days to figure out what will give me the best scenery. That being a non-deciding factor, it will depend on the plane. Most Airbuses tend to have the seats a tad further away from the wall, so on those I will choose the right as it gives me more maneuvering room with my right arm. 737s and 767s however are different - I will often choose the left because they are too close to the wall.