Obviously a ground floor room is best for escape, but they have other problems and are rare. My understanding is the best floors are 2-7. Mainly because most fire equipment can only reach to about that level. But you are not at ground level so if there is a street level explosion or somebody wants to break in to your room the will have a harder time coming through the window. Generally speaking I think it is safe to say for ESCAPING, lower is better. However from a security (terrorist attack or an B&E) stand point you don't want to be too low. Also don't dream of rapelling without some instruction first. I can't recall any instance where someone repelled to safety out of a building (independant of Rescue Service), that is not to say many folks would not have liked to have the option.

Marc