Always with a loaded chamber. Most gunfights happen at contact distance, which means that there is a strong likelihood that you will be using your support hand to ward off an initial attack. Until you get a round in the chamber, your gun is just a clumsy impact weapon until you can free your off hand up to rack the slide. Yes, it is possible to rack the slide one-handed, but I challenge you to achieve it efficiently while your concentration is on the guy trying to bash your skull in or stab you to death.