First off, get a gun that is small and light enough for you to want to carry all the time if this is going to be your carry gun. A carry gun will only do you good if you carry, no point in buying something that is going to be to heavy and large to carry even if it is a badass gun. I'm also assuming with this your going to be concealing, rather than open carry.
Also, go with Cor-Bon DPX rounds for your carry ammo. Shot placement is paramount, not the caliber of the gun. A .380 is not a bad cartridge either, it may not do the 12" of ballistics gel penetration with all loads, but the DPX rounds are suppose to do it. I don't care how big of a man you are, two or three round properly placed in the chest are going to stop someone no matter what the caliber is.