After 16 years of CCW and having carried everything from a full size SIG 226 to noisy crickets like the NAA Guardian and several 1911's I can tell you that the most effectively concealed weapon I've yet totted is my Kahr PM 9 carried ITP in a belly band rig w/1 back up mag.
This gives me 14 rounds of 147 gr 9pm in a package that is shootable, concealable, and of adequate stopping power assuming well placed hits.
It took 12 years and about 7k spent on guns and holsters to reach this conclusion but it was a fun journey and one I do not regret.
A former draw back to Kahr pistols was the price but their new CM line puts them right in line with other builders. Google PM9 VS CM9 for an explanation of the differences between the 2 lines. Personally I wish the CM's had been available 4 hrs ago when I got my PM. Could have saved $250 and had just as good a gun.