When I finally started thinking about buying a Glock I anticipated that my only use for one was going to be as an occasional off-duty weapon. For me, that meant something reasonably medium-to-small. I have to carry either a full-size or a compact pistol at work every day, and I prefer to carry something a bit smaller on my own time. I've spent many years carrying full-size guns, both semiauto pistols and revolvers ... and I still do, sometimes ... but I've also accumulated a number of smaller framed guns that work well with my preferred carry methods and body size.
However, I also wanted to minimize any potential loss of accuracy, effectiveness and controllability, as well. A finely crafted balance, as it were ...
Of all of the Glocks I've handled and shot over the years the only ones that really appealed to me ... for small off-duty weapons ... were the G26 or G27.
Between those two I preferred the G26.
I bought G26 and haven't regretted it.
I also bought a barely used G27 after I picked up the G26. I hadn't planned on it, and only did so because the price was simply too good to pass up. I've actually fired more rounds through my G27 than I have my G26, but only by a few hundred rounds, and only because I've been spending more time working with the G27. It's increased recoil impulse makes me work just a bit harder to control it, and the only way to do this is to practice with it.
If I only were going to keep one of them?
It would be the G26, hands down. Everything I can do with the G27 I can do faster and more smoothly with the G26.
I can't compare the G26 to a K9, because I don't own any Kahrs. Just a personal foible.
Comparing the G26 to my CS9, 3913 & SW99C 9mm, however, the G26 is very close in overall size and practical carrying weight to my CS9 & SW99C. Accuracy & functional reliability is similar ... which is to say good.
Some of the more obvious differences between the G26 and K9 include weight, grip frame design/angle/dimensions and trigger design ... so you really ought to compare them yourself by shooting the G26.