Aguila Ammo makes a 60 grain sub sonic .22
Are you familiar with the company or the ammo?
Paint me a bigoted Neanderthal, but I would prefer my ammo, if it has to be imported, made in Central or Northern Europe.
It is often said that .22's have killed more people than any other caliber. They may not stop a person determined to do you harm, but they may eventually kill them. Israeli execution teams used .22's after Munich.
How deadly depends on what you are hoping to kill. The smaller the varmint, the lighter the bullet. Hollowpoints are deadly but they make a mess of the meat. For larger varmints the Aguila Sniper Subsonic, which I have used, does nicely IF you are a darn good shot (head or other vital organ). The heavier bullet penetrates better -- but only if shot from a rifle (a revolver does not due justice to any .22 LR).
If you are set on .22LR, then the above suffices. If you want a .22 rimfire (especially if your local, state or other government has rules or regulations against centerfire), then the .22 magnum (WMR) is the best way to go. There have been lots of poachers of deer which have used .22 magnums because they are quiet. But they're not as quiet as .22 Sniper Subsonics. Close stalking and acccurate shot placement are crucial. If you're good at those skills then maybe archery would be the way to go (but you can't stuff a bow in a holster under a jacket).
the only aguilla i'd buy is their colibri ammo. shoots really slow, its very quiet, and you can shoot it anywhere.
if you're considering subsonic ammo, i hope you're planning on using it in a manual feeding gun (pump, bolt, lever, etc) because most semi-autos won't cycle subsonic rounds without modification.
gotta watch the bulk stuff you buy tho. the federal bulk packs is really hit or miss for quality. i went thru a number of boxes that was very good, but occasionally i'd hit a box that was junk.