[45Gunner]

I also vote for the second floor. If there is only one way in, there is only one way out. Tactically you are defending one point where the first floor presents multiple areas, door (s) windows, air-conditioning installation, etc.

For just a bit more clarification, you are defending only one entry point, the door. With your back against the wall, you have the clear shot. Chances are most perps will not deal with a second story as they too realize the confinement.