Penetration is most important in the "weaker" calibers. Not all shots are at a full frontal. Some are angled, or must penetrate bone (arm).
XTP bullet or Lehigh defense 90 gr. extreme penetrator show up well on tests. FMJ would be my much poorer next choice.
I am not laughing at the Kel-Tec .32. I have one in my car for back-up using the Lehigh bullet.