Personally, I'd use FMJ for any mouse gun with a caliber of .380 and under. I'd only use JHP for 9mm and above.
To me, If I were to pick one being superior over the other, I'd go for penetration.
If the bullet expands fully, but doesn't travel far, what good is it in the end? Not much good to me, personally.
If the bullet doesn't fully expand, but travels far, then there's more of a chance of hitting vital organs and/or the BG's spinal chord; especially if you're shooting a guy with a lot of mass (muscle or fat)? You NEED good penetration much more than good expansion... imo. If for some chance it actually exits (unlikely, imo, with a .380 and under) it's not going to go much further afterward. Plus, an exit wound is 3-4 times worse than an entrance wound, so that's just more hurtin' on the BG... which is good!
Go FMJ for self defense, if you ask me.