It will have to be decided by your preferences on this one. Both are fantastic firearms. I chose a K-9 over a Glock (G26 in my case). My reasons were:
1. K-9 grip was MUCH better for me (I have smaller hands)
2. Thinner for CCW
3. For defensive use, I liked the longer, slightly heavier K-9 trigger pull. Others might prefer the shorter Glock pull.
4. It's a personal failing, but I can't get used to a plastic gun
There is just something about my electroless nickel K-9 with Hogue wood grips...
I forget what the weight of each is loaded, but I don't think there is much difference in weight between a fully loaded Glock and K-9. The Glock holds more rounds though, i.e. the K-9 is a little heavy for it's capacity/size.
If my reason #4 doesn't apply, you might want to look at a P-9 also. The P-9 grip is not as hand filling as the K-9, but it gives new meaning to light and thin CCW. Also try to rent one of each to help you decide.
Enjoy your choice. Hard to go wrong either way!