Depends on what I have in my hands. If I'm not carrying anything then I'll take the stairs but if I have something that I need to lug around elevator here I come.
Stairs to go up, unless it's a lot of floors - my dad's an elevator mechanic and I've heard some horror stories (about how long people were stuck....not anyone falling or anything like that), and I just don't have the time to spend an afternoon stuck in one of those things. I also always take the stairs down.
umm. depends. In school I would take the stairs because only handicapped kids and profs took the elevators and I didn't want to seem lazy (although the elevators are for everyone). If I'm carrying luggage I'll take the elevator, or if I'm tired, but usually the stairs.