Depends if you're traveling solo or not - if I'm traveling alone (most common), I take window specifically to give me more room / support to nap. If I'm traveling with one other person (second-most common), we take the side with two - relatives don't care much if you lean on them a bit. So, I get the most space by taking the window and avoid strangers leaning on me I take the side with two when traveling with a companion.

Short flight where I stay awake - don't really care much anymore.