Which caliber is best for concealed carry .38 .308 .45 .40 9mm?

The BEST firearm for concealed carry is the firearm that YOU can carry comfortably, and use effectively. The .308 is a large rifle caliber, and generally not a concealable weapon. Many people will have difficulty concealing a very large firearm, such as a .45 or .40- although some people do. The .380, .38/.357, and 9mm seem to be popular calibers for concealed carry.

Bear in mind that, when carrying a concealed weapon, there are factors such as overpenetration of the target to consider. While you may be allowed to carry a .41 or .44 Magnum, it is not necessarily recommended.

Personally, I carry an XD45. It is a subsonic round, with substantial knockdown power, and a reduced risk of overpenetration (which is not to say that it couldn't happen). That works for me, but it may not be ideal for you. You should go to a range which rents handguns, and use that to help determine what feels right for you.