Aisle. You can lean away if there's a smelly fat guy next to you, signal for drinks, get up to the bathroom, I can't sleep anyway, flirt with the hottest stewardess, and planes never fly over big cities anymore anyway. Window is still okay I guess.
The guy who invented three seat plans (like who travels as a triad in the first place?) should be hanged.
Edit: though having talked to a number of stewardesses, apparently a lot of them like to fart when they push the cart, because their ass is exactly at head height, and nobody ever suspects them. This would argue in favor of the window seat. Unless that's your fetish of course.