I would choose 9mm any day. Cheaper rounds means more time on the range = moe training. Few people have the skill to shoot a .45 with predictable accuracy, again and again. Some of the high velocity 9mm rounds are amazing. Lets keep in mind, the much maligned and "weak" .38 accounts for nearly 50% of all gun related homicides in the U.S. Shot placement is the key. A centre of body mass hit with either calibre has very high likleyhood of stopping assailant. Lets keep in mind, the mere presentation of a firearm of any calibre is a fight stopper over 99.998% of the time. Ask any cop, most will go a career without ever firing a shot on duty, but will tell you of the de-escalating effect drawing a firearm has.