I'm pretty much a revolver guy but last year I got the "itch" for a 22 LR semi as I go to the range with friends when I'm in AZ for the winter. I wanted the Ruger MK III "standard" with the shorter tapered barrel - I couldn't find one for love nor money in any of the LGS. I did find a blued MK III Target with the bull barrel. It shot great right out of the box and is a lot of fun to shoot. I've never had any issues with it - it operates smoothly. I own a number of Ruger handguns and love 'em all.
This last week, I had the chance to pick up one of the Sig 1911-22 semis. I think it is a well built pistol (same as the GSG) and most that I have talked to that have one really enjoy them. It was on a special and I snapped it up at $299.99. I'm looking forward to getting to the range with it this week and try it out. I do shoot some paper but mainly just "plink".
At the time I purchased the Sig, I compared it to the Colt 1911-22 (made by Walther) which ran more money. I haven't taken the Sig apart yet - the only drawback I see is the darn set screw that has to be removed to remove the barrel for strippng down. But, maybe it's more of a pain than I am imagining. Fortunately, I brought out a 1,000 rounds of 22 with me as there are none available where I'm at right now. I think we'll all be glad when this "shortage" lets up.
At the same time, I looked at the Ruger 22 semi auto (the smaller polymer). As much as I love all of my Ruger handguns - I had prejudged this model before even handling - thinking it was too small. After looking at it, I also fell in love with it. At the time I looked at it, I talked with another customer who had one and he loves his - eats anything he feeds it. The salesmen put on one of the magazine extensions for me to try and it felt even better that without it. At some point, one of these will be coming home with me. Not a larger, heavier one like the Sig 1911 but a nice size for plinking and carrying on the belt for woods walk, hiking, etc.
I think some of the others have also made some great recommendations. I don't think you can go wrong with any of the Ruger semi autos 22 LR. I've handled the Buckmarks but never shot one. They have some good reviews and I think they would be a nice target/plinker to have as well.
Personally, I have mixed feelings on the Sig Mosquito. I've handled and shot one that my friend owned. It was finicky on ammo and I hated the trigger on it. He ended up getting rid of it. Others like 'em though so I guess it's a personal thing. Before buying, I would certainly rent what you are interested in at a range and try it out. Chances are, you are going to run across a number of different brands/models that you like - then the hard part is deciding! Good luck and enjoy!