Aisle, on all flights if possible:

1. That way I can drink as much as I want or need and get up without worrying about climbing over bulky or sleepy seatmates every hour to get up (once per hour is my average if I have a glass or two of wine or coffee and take my diuretic blood pressure medicine . Once on a red-eye where I got stuck at a window on an upgrade, I unfortunately landed in my sleeping aisle seatmate's lap in a very compromising position when I was discretely trying to climb over him and we hit some turbulence at an inopportune momemt.

2. I can access luggage in my overhead compartment as often as I want (e.g., computer, extra clothing, etc.) without having to carefully plan ahead what I will need.

3. I can stand up and get out of the plane faster when we're late arriving and I have a tight connection.

4. I can "people-watch" more from aisle seats when I'm bored.

What I don't like about aisle seats is that the under-seat storage space in front of you is often very small so I can't fit in my computer backpack or small carryon, have to use the overhead compartment which doesn't always have room by the time I get on. And of course I always carry a change of clothing in case the FA or kid running in the aisle spills something on me (I've been assaulted by water, wine, pasta sauce, a slurpy, orange juice, and a mud-covered kiddie backpack, among other things