I prefer the aisle if it's on the side of the plane, specially if it's a 2 or 3 seat config.

I dislike the middle seat in a 3-seat config, and also dislike the middle 4 seats unless they're empty.

It was easier when I was single, i would pick window or aisle. Now wife also flies so 1 of us would be in a middle seat........usually her she doesn't mind....I get the aisle....