I generally sleep best when I'm on my back or occasionally my stomach. Although sometimes I'll wake up to find myself in a "legs folded over self in the air like a dead bug" pose for some reason. I also have a tendency to wake up drenched in sweat even when it's not particularly warm.
Also, aside from occasions where I'm in close proximity to other people, I always sleep naked. I ditched the clothes almost instantly when I learned just how comfortable sleeping naked can be.