Everyone has their preference of whether they think a window seat or an aisle seat is better. If you are allowed to choose, and especially if you are on a long-haul flight, consider this one important point:
On long-haul flights, people like to sleep. If you travel alone and you get a window seat, you'll have to wake up the people next to you in order to get to the bathroom, and they'll have to get up again when you come back.
Of course the majority of people don't mind doing this, as it is common courtesy. But you can save yourself the hassle by taking an aisle seat.
Also, if you need to use the loo and you're stuck in a window seat, and the people next to you have their laptops or dinner trays spread out, it will be a big hassle for them to arrange everything for you to get up to use the restroom. Like I said, most people exercise common courtesy on these long-haul flights. But sometimes you just want the freedom to get up and move around as you please. :)
