I pick high floor because I want to avoid large groups on weekends (i.e. youth sports leagues, wedding parties, etc.). I stay mainly in suburban areas where outside noise is not much of a factor. However, 20 people deciding to run around, yell, make noise at 4-5 am when I am trying to sleep would piss me off to the point where I'd be willing to commit some serious felonies. Also, I don't like being on the first or second floor because it is easier to gain access at many properties without a room key, especially at limited service ones.

I can sleep through sirens, airplanes, and freight trains. I can hear the planes at the Renaissance LAX (they have good insulation but I can still hear them when I am awake) and can definitely hear the freight train in downtown San Diego (it is quite loud by the Grand Hyatt and Marriott Marina but I slept through that and leaving my TV on). Actually, the sirens by the JW Marriott in SF seemed more noticeable to me as noise, but I slept through that as well in a past stay.

Also, I have a fear of heights, but I can move down stairs quite quickly, so fire does not scare me. I actually prefer to be near the emergency exit, rather than the elevator (reduced noise and a quicker jump to get out if there is real trouble).