I faced the same questions about two months ago.
I wanted a gun where I could get all three non-trigger fingers on the grip. And 1/2 inch shorter barrel doesn't mean more concealable to me. So I decided against the PM9. (But if you really needed a really concealable gun that wouldn't kick much the PM9 would work well.)
The CW9 is a "less expensive" version of the P9. From the Kahr website: "The main differences are that the CW Series have conventional rifling, instead of match grade polygonal rifling; the CW Series have a MIM (metal-injection-molded) slide stop lever, instead of a machined slide stop lever; the CW Series cannot be retrofitted with night sights because the slide does not have a front dovetail cut; the CW Series slide have fewer machining operations; and the CW Series have simple engraving on the slide instead of rollmarking; and the CW Series are shipped with one magazine instead of two." At an MSRP of $549 verses the $739 it is $190 cheaper too.
I choose the P9 and found a new one for $539. It has been great.