My personal experiences have shown me that a .45 caliber round into the upper chest area on one side or the other actually spin a man completely around while a 9mm is equal to a good punch in the frontal shoulder.
Given a choice, knowing that I will be defending myself against an armed attacker, I will always select a .45 caliber.
Now when the additional factors of personal comfort are added into the situation of carrying a handgun whenever I leave my home, I would select a .25 caliber knowing the odds of having to use the weapon are slim. Weighing comfort and effectiveness knowing that I would rarely be inclined to shoot someone more than 30 feet away from me I will select a S&W Chiefs Special in .38 caliber.