the real question at your size is, how do you want it to look? couple that with, which SS watch are you after exactly? if you're after the leather loop (i only tried one on after I got my watch, and I loved it but I don't think its practical for me because i often get my wrists wet or might have my daughter sick up on me) then you're stuck with the 42. if the milanese loop is your cup of tea, the way the band attaches to the watch make it seem a little longer across your wrist than other band options and might distort how you see the watch on yourself - the 42 might also be close to overhanging your wrists and forming a D shape (flat on top with a weird U shape bracelet underneath, like a bicycle lock) which I don't really like at all, but others don't see a problem in that. similarly with the sports bands, I didn't like the way the sports band sticks out over the edge of my wrist with the 42, where it curves more nicely with the 38. the shape of your wrist might also affct how it sits, when i had a 38 sport i had the chance to swap for a 42 and hated it, because it instantly felt awkward. the heavier SS 42 with a leather loop, however, fit perfectly - i think the sports band jjust couldn't hold the lighter sport down against my wrist properly.
i guess the point of this ramble is, you really have to try them on. there's so many factors at play you can't get from a flat paper cutout. some people need the 38 because the 42 is bigger than their wrists. some people need the 42, because they have fat fingers. for others, it's a case of how you want it to look - and like i say, that starts with the band. i went with the 38, myself - partly due to my preference for that size with the milanese loop but partly because both it and the second one i ordered as a replacement (it was for my wife to begin with) arrived much quicker than the 42mm space grey i'd ordered after the first try on session.