Just to kick to Hydguy's side.. I agree with the smaller, can be better. I come from the logic that shot placement counts for more than size.
Without hard numbers to back me up I will not spout some number about how great X caliber is compared to Y...
Sure the story of some guy who took 3 rounds of .32 and kept on comming is out there. I have seen dashboard video of a GA state trooper who put several .357 rounds into your average pot bellied man. The perp took out a .22 and killed the trooper, there are no absolutes.
If you want something that is small and functional, don't limit your options. The tiny .380's are hard on the hand. They are almost all pure blow-back, and don't weigh squat. It feels like you are shooting a hand cannon! I don't like to shoot the Colt pocketlite2 as it feels like I am shooting a 1oz 12GA slug out of that little thing.