Just purchased a Ruger SR22, .22 caliber.
Small, lightweight, loud bang when it goes off, very small kick, which allows for more accurate placement. I used to have a Walther PPK .380. Way too stiff in all regards. I could have taken to a gunsmith to have them reduce the weight pull on the trigger, etc though in general, its a cute weapon that is just less effective. Also, the cost of .380 ammo is much, much higher than simple .22.
Also, the Walther has a .22 caliber that is actually slightly lighter and smaller than the Ruger, and from what I hear a great model. The biggest difference, the Walther and the Ruger is cost, the Walther is about $75 more. My little Ruger, with tax was $300 brand new. It also has a threading option for silencers, which sounds fun though I'm not James Bond type so no need of a silencer. Actually, the opposite. Having a weapon ends 99% of any situations, and if you had to pull the trigger a big, loud bang should cause them to piss their pants as they run. Though if it must be, the small kick allows for very accurate round placement. No knockdown but placement kills just fine. If you want knockdown you're going to need a model 1911 .45.
Just my two cents.
boo