Coz,
I have owned both the HS 2000 and the Kahr. They are both great guns with better accuracy than most people are able to use. That said if you are looking to carry it concealed I would go with the Kahr.
The HS is roughly the same length as the G19 and the same height as the G17. The HS has good accuracy and a good SA trigger (fairly light and somewhat crisp). The sights are interchangeable with NS fitted for the Sig 226/228 line. The finish is not what I expected from reading the gunzine articles who raved that it was similar to the tenifer treatment of the Glock (It most definitively is not). You really have to remember to wipe the gun down with oil after you are done with it. The craftmanship is pretty good on mine. Some users of the HS have mentioned problems with extractors using the Value Pack Winchester White Box available at Wal-mart (and Gart Sports if you are from the NW). I have never had a problem with extraction. You can learn more at
http://www.hs2000talk.com . I understand that the Springfield XD is also available in 357 Sig and 40. I really like the design.
The Kahr is significantly smaller. I have been carrying daily for the past 4 years and have carried several guns. Generally the hardest part of a gun to conceal is the butt or grip of the firearm. I usually find that the thinner the gun the better.
In the Kahr you get a good combination of thin frame and relatively short grip. I currently own an MK9, it is probably the most concealable 9mm that I have ever seen. Comparing the MK9 and the K9 I think that the K9 is the better shooter by far but the MK 9 is the easiest to conceal. The downsides to Kahr are the finishes. I had my Blued Kahr start to show corrosion after a day of carrying in a nylon IWB rig. To me the stainless finish is the only way to buy a Kahr. Also the standard trigger on the Kahr, while smooth, is difficult to shoot rapid fire (I have no experiance with the Elite Trigger). The first Kahr I owned would not take my reloads due to a very tight chamber, my current Kahr will take them.
I think you would be well served by either gun but the Kahr is more concealable. The subcompact Glocks would make the comparison much tougher, they really are a good concealment gun too. Good Luck,
-Coug