Like the others have said, carry and shoot what you shoot the best and are most comfortable with. I keep a .357 mag by my bed and a 12 gauge in the closet but the gun I keep in the bag is the 9mm. Ammo is cheaper, I can afford to shoot a lot more and I feel confident with it. My son shoots a 40 and he is very good with it, I certainly would be happy to have it if I needed it. The what caliber is best debate could go on forever, everyone has a favorite and its usually what THEY shoot best.