The question is a big one.
We all should examine this question, from our own point of view. It is an important question.
The .40 S&W was invented to fill a need, in my my mind, a non existent one, the .45ACP does the same job, and it is here. And has been for over 100 years, low pressure, new bullets, it works.
All of it to make the mess that the FBI Gun Fight turned out to be, the fault of a bullet!
But no one has ever convinced me, and never will, it is where you put the bullets, as many as possible that counts, I like a lot of 9mm, you can pick what you please.