The Kahrs I have first-hand experience with are definitely a mixed bag as far as reliability goes. My P380 has provided a pretty maddening ownership experience thus far and is on its third vacation to Kahr since mid-April.
I've only shot two of the Rugers -- an SR9 and an SR9c. Both were perfectly reliable in the 200 rounds I put through them, and I have read no complaints about their reliability elsewhere, nor have I seen any issues in person. Complaints about unreliable Kahrs are pretty common; just run some forum searches. The trigger on the SR9 trigger was pretty bad, but the SR9c's trigger was good. My understanding is that all SR-series guns come with the upgraded trigger now.
The Kahr certainly has more cachet and style, but if I had to bet my life on the reliability of one over the other, I wouldn't hesitate to take the Ruger.
My suggestion would be to add another pistol to your list and take a look at the Walther PPS. It's more expensive than the two you've mentioned, but it's easily the finest single-stack, ultra-slim 9mm/.40 in production, in my opinion. Save up for an extra week or two. Fit and finish of the other two pales in comparison. It's totally reliable, easy to conceal, unbelievably accurate, and very soft-shooting for its size.