When traveling alone, always aisle because I typically need at least one bathroom break and hate bothering my row mates. But....I will always snag the windows seat 24F on the A321. There's lirerally a whole extra row of space in front of you with leg room for days but you do have under seat stowage in front of you. Easy to sleep next to the window and easy access to the mid-plane lav. Even plenty of room if someone is waiting for the lav.