I own the MK9, the PM9 and the K9.
I got the PM first and have shot it quite a lot. One day, during a structured training, I fired about 450 rounds thru it. The recoil is ok for me. In fact is surprisingly tolerable for such a lightweight piece. (Not true with the PM40.....man, that recoil is pretty nasty).
I find that I can shoot the MK9 better however. And that is no small matter to me. The recoil on the MK is even easier since there is a substantial weight difference. So I prefer the MK but only for belt supported carry. It is just too heavy for the "deep" front pocket carry I do in summer. It might be ok for rear pocket carry (not my cup of tea)....
The K9 is similar to the MK (a bit longer in the barrel and a bit longer in the grip, but not much). I shoot both about the same, with a slight edge to the K9.
Both the MK9 and the K9 are much classier looking and, to me, feel much better in the hand than any of the Kahr polymers. You also have the ability to experiment with different grips, including laser grips...at least for the K9. You can put a laser on the PM, but not a grip laser like Crimson Trace.
The PM can't be beat for pocket carry, except by a smaller piece in a lighter caliber. When belt carried, which I almost never do, I hardly notice it all.
I had always thought that I would keep only one of the three Kahr 9's after giving each a long fair trial. But I find that I like each of the three so much that I will most likely keep them all.