No one caliber is best...
Kimber uses the "Ultra" designation for their guns with 3 inch barrel, and for the 4 inch guns they use the term "Pro". Either one is quite concealable for carry.
Originally Posted by golfer
I will carry different calibers, including .45, .40, 9mm and .357 magnum depending on the situation and the gun I want to use. I believe that all of these 4 calibers can be effective at stopping a threat if you can shoot well enough to put one or more shots in the center of mass.
The most important things are to have a reliable gun that you trust, practice frequently, use quality hollowpoint ammo and know the laws in your state.
The gun I use most frequently for carry is similar to your Kimber: