I used to really like single stacks for CCW in the summer, particularly my Beretta Nano. I have considered picking up a Walther PPS, too. But my HK P2000 has pretty much lead me to putting the Nano in the drawer. The Nano is a little bit thinner but if you lay it on top of the P2000 they're virtually the same height and length. IMO it's the height of the gun (from the top of the rear of the slide down to the bottom of the mag floorplate) that dictates how easy a sidearm is to conceal, not really the thickness. There are a few circumstances where the thinner gun is a bit easier to conceal, especially in very hot weather, but for the most part they're about the same. But I feel a lot more confident in the HK carried 13+1 than the Beretta with its 8+1.

Sorry for the digression! I realize this isn't a gun forum but it's hard to discuss EDC without mentioning a sidearm, at least in my case.