The best loadings for the 9mm are typically in the 124g+p loadings or the 147 gr. Both loads roughly perform the same in ballistics gel. The heavier 147 gr loadings(given similar bullet designs) often favor penetration over expansion. The 124+p often favor expansion over penetration.
Personally, I prefer to shoot 147 gr loadings like the pdx1, hst, or gold dot. 147 gr loadings tend to be light recoiling, quieter(not supersonic and less powder tends to have less wasted blast out the muzzle), and again...favor penetration. In the world of handgun terminal ballistics...
shot placement>penetration>expansion. Light recoiling makes it easier for rapid-follow ups and more controlled shot placement. The heavy-for-caliber 147 gr also favors penetration, with many loadings getting 14-16" instead of the 12" of 124+p loadings. Standard pressure 147 gr loads are also easier on the internal parts of the gun.
The big drawback is they often have a longer OAL and may not work in all firearms. My m&p9c has ran flawlessly with any 147 gr load I've fed through it. My current load is actually a combination of both worlds....the underwood 147+p gold dot load. tnoutdoors9 did a test on these that was pretty impressive. My personal tests generated the same results as him. It's hard to argue with .8" expansion and >12" penetration from a 9mm.
As always, shot placement in defensive loadings is the #1 priority. Handguns only crush a permanent cavity through what the bullet touches...the temporary cavity really only does damage through inelastic tissue like brain/liver. You need to put that .6-.8" x 12-16" hole through something that bleeds a lot to stop someone quickly. They'll bleed out, go in to shock and pass out. Alternatively, you could get lucky with a CNS shot that cuts off the signal to their skeletal-muscular system...but that's outside the realistic realm for most in defensive shooting. The spinal cord is about as wide as your thumb on the very back of a person's body, wrapped in thick bone. The brain is the size of your hands put together...again wrapped in bone. Actually making an aimed hit on either of these targets is not a very realistic possibility. Center-mass shots through things that bleed until the threat stops is generally the best practice.
