I prefer the left for some unknown reason. Although, I just really like any aisle seat on either side of the plane. If I am on a DC-9 or MD-80/90, then I like the side with two seats if I am in the back. Of course, if you have to ride in the back of a DC-9, I love being by the engines. I just love hearing the noise and cannot get enough of that sound, because we will not be hearing it much longer.