I am still forming my opinion but I like the sig as of now.
For what it is worth, I just purchased a real nice sig package from a TGO member last week. I sold my Walther P22 to make the deal happen.
I purchased a used Walther a couple years ago and was pretty happy with it but hadn't really shot it too much. The gun was pretty picky on ammo and had a tendency to jam. That all changed after my first NFA aquisition. With the addition of a can, the gun functioned flawlessly. And was more appealing to shoot. After now shooting it a good bit, it became less appealing as the accuracy became an apparent issue. I wondered if it was me or the gun and I puchased the factory laser. The laser proved to me that it was not my inability to command the firearm. I did some tests and found that it likes wildcat ammo for best group as well as penetration. This gun has the thinnest barrel I have every seen and I feel this has a good bit to do with it's accuracy. The gun is ok for plinking cans but it feels like a toy to me and that is where it stops. It is very light and without a doubt good for women and children to plink with.
I handled the Sig 22 and even put a few rounds through one a while back. I was wanting one to try out and put through the test. I was in agony while being out of town for a week while a good deal was listed on TGO. I claimed it upon my return. The gun was new and I was expectiong a break in period. After making my purchase I put 350rnds through it bufore the sun went down. It definately had plenty of failures with the slide not engaging the last 1/4" being the most common. I tried several brands of ammo for reliability and I have no opinion on that yet. The accuracy was good and I think an improvement over the walther. The gun feels better and the extra weight in the sig results in faster fallow up shots with less recoil. It didn't come with a thread adaptor so I have not tried it suppressed. I am hoping for better functionality with the addition of the can like I experienced with the walther, but I will not bank on that. I expect it to just take rounds down range to break it in.
I will post an update after I have some more experience with this sig. Assumeing that the raliability on the new sig improves and that the suppression level is on par, I can not imagine that I will ever regret my decision to switch from the walther to the sig.
I would be considering the Ruger mk very heavily in this decision. Very reliable and easily the most accurate choice for plinking.
Just my $0.02
Aaron