You want something that will penetrate. If you have a situation where your target has heavy clothing, etc. then you don't want the bullet exploding when it hits the surface of the clothing.
It all depends (and that three-word phrase could be the end of nearly any discussion). If you are planning to defend yourself at 200 yards on a windswept plain in Montana then your needs will be different than if you expect to defend yourself against multiple assailants in a sheet metal storage facility. For me, a more realistic situation revolves around a suburban environment.
Does your neighbour have the right to endanger, and possibly injure and kill, your family members because that neighbour is, legitimately or not, afraid of someone in her home? A person that that has nothing at all to do with you and your family. Or, do you think your neighbour should take all reasonable efforts, including choosing ammunition that has a lower probability (sorry, the risk never reaches zero) of harming your family, to prevent that harm?
Warning, veering off-topic, but still at least tangential:
This is part of the shame of the current false-safety movement. It makes it hard to discuss real safety without drawing ire from both sides.
Again, it all depends, there is no "best" because there is no single situation. However, we can start with a realistic assessment of the most likely defensive scenarios and building around that. If a realistic scenario does place you defending yourself at 200 yards on a windswept plain in Montana, or facing multiple assailants in a sheet metal storage facility, then you probably will make different decisions than I have.