I prefer the aisle. When my husband and I fly together we get aisle seats on either side of the aisle. Close enough to talk, etc but just a little more "space" for both of us
Have to have the window seat. I lay my head on the window and go to sleep. If I'm with my husband or someone else I know I don't mind so much having the aisle seat, but if I am alone - the window is a must - I'm too afraid I may wake up and find myself sleeping on the shoulder of a stranger!