S&W Model 18-3 Combat Masterpiece is my current favourite, probably will remain so. The Ruger Single Six stainless convertible that i traded off to buy my dad a model 617 gets an honourable mention.
i've shot the S&W 22A, 617, Ruger MKII, Ruger 22/45, High Standard, Browning Buckmark, S&W 2206, ColtWoodsman, Walther P22 and the beretta 92 with .22 practise kit as well. Currently I own the practise kit and the Model 18. I've come to the conclusion that .22s are for cheap low recoil practise, so I prefer them to be conversion units or sub caliber versions of my centerfires.