.22 silenced. The bullet will ricochet inside the brain causing more damage. If you've ever heard a silenced .22 go off, rain makes more sound, lol. I think a lot of Philly guys preferred the .22.
no doubt it has been used a fair # of times, but its a very poor choice imo for a bunch of different reasons.
#1 its a very underpowered round, and it may not even penetrate the skull, just ask john veasy. the problem is only amplified when the even weaker subsonic .22lr ammo is used with a suppressor.
#2 rimfire ammo can be very unreliable, especially in semi-auto pistols, and having a gun jam during a hit is never a good thing.