I don't have any direct experience with any of them but a friend (and fellow OSAer) has the Sig 238 and those are really cool little guns. Have not got to shoot his yet but want to!
I don't know if it's the best on your list, but I own the Kahr .380 - it *IS* the best among the really small ones without a doubt (among Kahr, Ruger, Taurus, etc.).
The Sig and the Colt are the same gun, I believe, and and very nice, but much larger - they fill a slightly different niche being larger. They're about the smallest you can go and still have the full-sized gun FEEL to them, or nearly so, and the attendant handling characteristics including practical accuracy under stress. Good stuff maynard, but the Kahr is what I needed for my SmartCarry - small and light as possible. I'm already packing a lot of bulk down there, so not much room left.
Of all the .380's mentioned, the CZ-83 is better than them all. Laserbeam accurate, good firepower, and steel so you dont get that sharp .380 muzzle flip. Try one, you wont go back after you do...
I really like the Sig. I'm not crazy about .380, but will probably get one just because I like the Sig so much. Great looking, feel great, and super reviews!