The SIG Mosquito, Walther P22, and the S&W M&P22 are all made by Umarex under license. The SIG and Walthers have very dodgy reputations. Oddly enough, the S&W does not but it also goes for a little higher and only comes with one magazine.
On the flip-side, the Ruger SR22 has almost universally good reviews with the only complaint seeming to be the trigger. Unlike the Umarex manufactured SIG and Walther, the SR22 does not seem to be picky about ammunition.
Bersa also makes their Thunder pistol in .22 LR and it also gets good reviews. It is also cheaper than any of the above. Frankly, if I were to make this purchase I would go for the Bersa or Ruger. The other pistols are too expensive for the problems they routinely have. Unless of course you enjoy only shooting mini-mags out of them, which seems a ridiculous compromise to me.