It depends on what you want. The Walther is compact, light-weight, has fantastic ergonomics and is easy to clean. The Ruger is larger and heavier, more durable, somewhat more accurate, less picky about ammo and a pain to clean. The Walther was designed to be a training companion to the P99 and behaves more like a typical defensive handgun than a target pistol. If you want a plinker or general practice piece, the Walther is great. If you want a target gun and shooting tight groups is your main goal, get the Ruger.
I've had a Walther P22 since November and have put about 2000 rounds through it. When I use CCI Mini-Mags or Stingers, the gun is 100% flawless. When I use cheaper ammo, its a crap shoot. Remington Golden Bullets typically yield a failure rate of about 5%. Some people will tell you that the gun is "crap" and that they all break, but that is simply not true. I can and lubricate mine after every range trip and I see no signs of wear at all. If something does break, S&W will take care of it and has good customer service. At this point, I have no regrets with my choice to buy the Walther.