I have shot a S&W model 22A-1, I OWN 3 Ruger MKII's. There is no better rimfire .22 than a Ruger; IMO of course. They can be upgraded, if desired, without great expense. But out of the box they are great to begin with. I was told once, and I believe it, they are over engineered and will last many lifetimes. They can be a challenge to disassemble for the 1st time, after that it is not a problem. As to the MKIII, I have never owned one, but from what I have heard the loaded chamber indicator makes it even more difficult to strip. I would stay with a MKII, although I really wish Ruger had offered the "Hunter" model in a MKII - sweet pistol. If you would like to research more about .22 rimfires check out www.rimfirecentral.com
. They know their stuff. Good Luck.