The C-series Kahr models have cost saving deletions, such as normally rifled barrel, non-polished/throated feedramp, longer 1/2" trigger pull, less slide machining and one magazine. The PM9 and MK9 are similar to each other, save for the frame.
Really it depends on your needs. I wouldn't get the MK9 for pocket carry, too heavy. That extra mass really helps with follow up shots though.
I have a K9. It's like an improved steel Glock with normal grip angle and better trigger.