They're both really good guns. I haven't owned any K guns but have shot a few. They are pretty nice. I do own a couple Sigs. I really like those. My opinion you really can't go wrong with either.
Not a lot of .40 fans around..I personally like the round. I think it's a good middle ground round between the 9mm and 45 ACP. It never took off like it was expected to I don't think but it aint going anywhere..heh. Good luck with your purchase and I hope we see pics and a range report whatever you get