S&W 442 with Eagle Secret Service grips. It's my second one,I gave my first one to my dad for the same purpose.
I'm pretty much set on autos for defense, butI haven't found anything to beat the 442 for a pocket gun.
It's light, and has an oddball shape to keep the "printing" down.
It hides OK even in jeans.
I keep it loaded with +P 125 jhp's.
Hammerless revolvers can shoot decent groups if you dry fire a lot to get used to the trigger.
I do occaisionally carry a stainless Walther PPK.
My alternate choice-and only if my pants are made of a material that won't hide the 442 is a Walther TPH. Yes, it's a .22, but it beats nothing at all, which is the only alternative if I'm resorting to carrying it anyway. Plus, being a .22, I get a lot of practice with it. Damn, that gun is accurate. In fact, it's almost worth carrying around just to keep it handy to show your buddies how well they shoot.