My dad owns a Walther PPK from back before they were owned by Smith and Wesson. He carried as backup weapon as a cop for years in the 80's, and still says it's one of his favorite guns. They are great guns; old and present models, they only down side is they are all steel, and quite heavy for what you are getting. When I worked at a gunshop, I messed around with our PPS quite often, and I really think they are quality firearms. Can't go wrong with smith and wesson brand firearms, but I would prefer a lighter and slimmer 9mm (PPS) to a heavier and harder to conceal .380 (PPK). Although walther is running a $50 of deal for PPK's.
As far as Kahrs go, I own a P9. I have put thousands of rounds through it and use to be my primary carry gun (until I got my Glock 26). I know a lot of people on this forum enjoy Kahr firearms, although they are not backed with the same lifetime warranty that Smith and Wesson firearms are. Fairly similar dimensions to a PPS though.