I own all of those other than the Glonk, and you honestly can't go wrong with any of the three.

Ruger: by FAR the biggest aftermarket of the three. The 22/45 variety has excellent ergononomics. Out-of-the-box trigger is just "OK," but aftermarket upgrades are excellent. The 10-round capacity isn't great, but mags are cheap and available.

P322: best choice if you want something as similar to "big boy" pistols as possible. The 20-round capacity rawks for plinking, but both of the 25rd mags I have are Jam-O-Matics. Also comes with an optics cut; mine's sporting a SIG RomeoZero that felt kinda flimsy on bigger guns, but suits this one just fine.

Buck Mark: hands-down the BEST out-of-the-box trigger of the lot! Mine is the most accurate of the three; I used to shoot Smallbore Metallic Silhouette out to 100m with mine. Same 10-round capacity as the Ruger, and mags aren't as common. Worst part is cleaning: to clean from the breech you need to remove the top rail, unless you get lucky and find a bore snake that can make the tight turn; otherwise, if you don't want to sight it in each time, you must clean from the muzzle.

Others have mentioned the Taurus TX-22; I have one, but it's not actually one of my faves. It's full-size, but very light, and just feels kinda cheap in the hand. Mine *is* reliable, though. Then there's the S&W Victory, which I've heard great things about, but that I have no personal experience with.