The Secret Service presently uses the .357 SIG, and although not my choice, their choice seems to indicate that there is nothing special about a crowd calling for anything different than an ordinary duty pistol.

One of Jeff Cooper's staff once said that a 9mm is like the .45 ACP on "stun" (a Star Trek reference). That statement was made in 2000, so 16 years of ammo development later, the 9mm is still trying to be a .45 ACP.

Therefore, get whatever duty pistol you are comfortable with. In my opinion, a 22 is not the answer.