For me, this depends on whether the stairs are out in the open or enclosed, where the elevators are in relation to other people and my car, and what level I'm on. Second level, stairs. Fourth or fifth, at night, probably elevator. If in an area where homeless folks are common, I'll probably avoid the stairs.
My logic is that under 3 stories, I can probably quickly make it to a place where I can jump, if absolutely necessary. I'm not overly fond of elevators - they're boxes, after all - but sometimes they're safer than they look.