I have owned both a ruger single six and the AMT automag. Both great guns. As far as I know they don't make the AMT anymore in .22mag, but they may have started again. I had the six in barrel model and it was pretty accurate and fun to shoot. The noise and muzzle flash was VERY impressive.
My single six was pretty nice as well, but I will admit I shot it mostly with the .22 long rifle shells.
Honestly, I wouldn't waste my money on a .22 mag pistol. Just get a .22 long rifle pistol and shoot stingers or velocitors out of it.
Paul