Still the 9mm and .40 S&W are two of the most popular calibers for concealed carry self-defense pistols. My take is that in a full size or mid sized gun the .40 is a great choice, but as you move down to smaller guns the .9mm starts to be the better choice. In my experience, and as recounted on various gun boards, when you have very small pistols the .40 presents both a lot of recoil and more reliability issues than the same guns in 9mm. If I were looking at something the size of the PPS your friend is, I think I would go for the 9mm version.
Among the many excellent ultra-compact 9mm / 40S&W pistols my favoite is the Beretta Nano. It's a bit smaller than the PPS.
The Nano is pictured on top of the Walther.
And as much as I like it, I still find I carry my Walther PPK/S more. However, I understand that they are no longer making PPK/S pistols.
