Single stack 9mm's are the popular guns right now. Glock 43/43x/48, Walther PPS, and S & W Shield. The Sig P365 is the new hotness, same width as Glock 43 but almost double the capacity. Carrying is more about holster and clothing than it is the gun. With the right clothing I can conceal my fullsize M&P no prob. I've been setting up and carrying a Glock 43 for last few weeks and I really really like how well it hides. I can carry it appendix at 12:30 with a +1 mag in it, and a spare +2 mag at 11:30 and not print even with an athletic cut polo on. Ammo selection and compatibility with your firearm is paramount. Most guys buy a box of hollow points and never really verify how well they run in the gun. Talk to any good defensive pistol instructor and they will tell you you don't know your gun unless you've run 100-200 rounds of defensive ammo through it, not just FMJ. You'll often find that these smaller guns can be a little picky with feeding hollow points. 1911s especially. I just shot 96 rounds of Federal 124 gr HST through my G43 this week. 1 failure to feed, which I believe was because I limp wristed the shot during a 1 handed drill. Defensive ammo may appear expensive, but you are betting your life on it so you better make sure it performs with the gun you intend to carry.