I usually sit and pick photos apart when trying to decide. Is it in sharp focus, are there any distractions, does the actual subject get my attention or is it something else that grabs it, is there texture to the photo, is it grainy, are there shadows, is there an overexposed area, those are the things I look for when I can't decide on just one photo.
i pick the one that's the sharpest and clearest pic that i took... then if i'm tossed up between the look of the pics, i'll ask my girlfriend for her opinion, and why. she'll usually tell me she likes A better than B because the subject looks better etc etc...
