I have both calibers and I carry one or the other all the time. I will say that I do have more confidence in the .38 special caliber over the .380 but mainly due to bullet weight. IMO, the perfect .380 round would be something in the 110, 115gr backed by the power from something along the lines of the BuffaloBore +p stuff. For now I'll continue to carry my 638 w/crimson trace backed up by my Sig P238, or maybe my S&W Bodyguard .380 stoked with the Buffalbore stuff in the heaviest grain configuration they offer so far.
I do believe that the .380 will easily do the job if used correctly and shot placement is good. My main concern with the tiny .380 autos is that the idiot that forces the draw might be so dumb as to think that the pistol doesn't really pose a deadly threat, so the first line of defense as a deterrent gets lost whereas when the revolver comes up, the rounds are visible for all to see.
Don't ragg on me for saying the deterrent thing. I'll always try to use/add every variable possible in most everything especially in important matters such as self defense.