"Most" reliable.....?
Both, at their best, are superb. The good ones are, very, very good. If I had to choose, I would say, all things considered, the Sig. Except sometimes, when individual, particular guns are not. But in the aggregate, I would choose the Sig over the Kahr. Especially the older Sigs over some, but not all of the Kahrs.
I own three Sigs and four Kahrs. They are very, very different and have different missions. The Kahr does what it does much better in its little niche than probably any Sig. But you asked about reliability in the abstract.