space would be so lonely, there would be no other life forms, and you would be so far away from humanity. I've lived alone in a boat for about a year once, so the submarine wouldn't be to far of a stretch, I was still incredibly lonely.
Oh gawd... THAT is a tough one... I would rather do outer space, but upon further evaluation I would have to choose submarine simply because of the fact that you would loose muscle mass from zero gravity in outer space. Muscle atrophy is something I could do considering how little muscle mass I already have lol