I have never used either for self defense. I shoot both at paper targets every chance I get and they are both a ton of fun. I am quicker and more accurate with my 9mm but I smile more when I shoot the 40. I carry either the .380, 9mm, or 40s&w everyday and feel protected with all three. I have never shot anybody so I don't know which round works best as a man stopper. Maybe when I mature I will take a liking to the 45 acp but I will probably try out a 10mm next, just to say I did.