I have been wrestling with this issue too. I used to carry a NAA .32 guardian. 7 rounds and very small. It empties quickly and makes a nice rock to throw at someone.
I recently purchased a couple of bigger pocket pistols in case I would ever have to get one out of my pocket.
I got the PM40 and the Glock 33. Both are very accurate. Both shoot pistol targets great at 25 yards which is much more than I need for a pocket pistol. The Glock 33 in .357 sig causes more hand wear in shooting sessions at the range, but it holds 10 rounds. I actually replaced my 6" 686 with it in my vehicle since I can drop the Glock in my pocket.
All that being said, the Glock 33 is too big to put in my pocket for any length of time. The PM 40 is at the edge of too big. I think the PM9 is probably as big of a pistol as I would want in my pocket on a regular basis.
I skipped over the .380's for the same reason I have retired my .32 to the safe.
I used to carry the NAA Guardian .32 as well. It's about the size of a wallet, and I'd slip it in my back pocket. It's really a backup gun suited for a worst case, better than nothing situation, as it's not terribly accurate and you aren't going to be drawing it out quickly. However, it's sturdy and simple construction, and while one of the magazines went bad, I never had an issue with the gun itself, and I didn't clean it nearly as much as I should've. It's heavy though.
I also carry a Sig P238 in my front pocket. I love that thing. I do occasionally carry a Bersa 380CC in my pocket, but only when I've got a bit of room like when wearing coveralls.
I really like my kel tec p32. I personnally like the recoil characteristics on it much better than .380, it is cheap to get quality ammo to shoot, and after 200+ rounds, I have yet to have any problem.