Caliber (and bullet choice for that matter) are primarily an academic exercise for anyone who is not a LEO / MIL and those guys are mostly issued a weapon and ammo and have no say in the matter anyhow.
A 115 grain 9mm FMJ in the right spot will stop the threat. I like heavier bullets because they carry the most momentum to punch through things that might need punching through. To that end, I have a habit of selecting rounds that are more on the heavier side for each caliber I own... thus the 180 in the .40 cal.
Personal choice... YMMV
Gen 4: 17 (9), 20, 19 (2), 21 (2), 22, 26
You are on your own out there... Act Accordingly.