This is very subjective. I don't think there is any one best concealed carry 9mm. I believe it's what fits your personal wanted and needs best. There are a lot of really good firearms already mentioned above, but I believe no one handgun is best for every carry situation. I carry my Ruger LCP most often, but when I step up to 9mm I currently carry my FNX-9. I used to carry my Ruger SR9c, but that went, when I was forced to thin the herd during some hard financial times. I am in a rebuilding phase and am trying to optimize my purchases. My next compact will more than likely be a S&W M&P40c. Let me explain. I am leaning this way for several reasons.
- Size: The M&PXc series are all a really good size firearm and fit my hand really well, which is important. They are also shorter overall than a shield, although .2" wider. IMHO this fits the idea of a multi-role pistol the best. It is a good carry/hd gun as well as fun shooter at the range.
- Caliber: I am not a huge fan of 40S&W, but by choosing the 40c I can convert to 357sig with simply a barrel change, and 9mm with simply a barrel change and magazine change. 3 calibers in one. The cost is under $200 for the other 2 barrels and a couple 9mm mags. Much more affordable than purchasing 3 different firearms.
- Accesories: Do to the popularity of the M&P series the accessory market is large. It is easier to find accessories for these than some other models of firearms. Example, night sights & holsters are available from several manufactures, in different configurations. You are not stuck with 1 or 2 choices.
For me its all about bang for the buck now, and this particular firearm fits my needs and wants the best. Your mileage may vary.