FlyMeToTheLooneyBin beat me to it on nearly all counts; if you're certain you want a window, take 12J--same reasons as above, as meal choice is probably the only real differentiator. Note that you are almost certain to have a seatmate if you choose a window, whereas the 5 middle seats are generally some of the last chosen (as stated), so for best odds of getting an empty adjacent seat (which is very nice when it happens--good place to put your pillow and blanket when not in use, or your shoes/laptop bag while reclined to sleep), go middle. If you must see the word as you fly by for your heart to be content, go with 12J. As my looney friend pointed out, most people will break left for both lavs and deplaning, plus FAs tend to prefer to go up and down the aircraft on the port side, so I generally choose starboard when possible. Also, and this depends on the FAs you have, the J cabin is generally split with A/B/D/E seats being served by one FA and G/H/J seats being served by the other, giving a slightly better ratio for those on the starboard side (there are 20 A/B/D/E seats vs. 17 on the G/H/J side).