I owned both a Kahr CM9 and a S&W 642 until I went crazy and sold my S&W 642. Both weapons have different advantages, based largely on my experience with my 2 and my personal opinions.
J-Frame- PRO: no slide to rack, more ergonomic, (almost) never malfunctions, easy to carry IWB/AIWB. CON: Reload time, number of rounds, malfunctions tend to be catastrophic
Micro 9- PRO: Reload time, easy to carry multiple reloads, malfunctions easier to overcome. CON: Ergonomics, harder to grip/draw from holster, slides harder to rack, more limited locations for IWB holster placement.
Again, these are just my 2 cents. I like both, and will probably end up buying another J frame/LCR to add to my CC options.