It's the short one that comes in this set. And yes, Apple CCK.
Do you hear any difference between this cable and the stock usb one?
I'm now using a Lindy premium gold cable with my uS, which I find a bit harsh. I also quickly a/b tested it against another shortest cable lying around: although being skeptical, I found the latter quieter than the lindy with the iMac volume and the played track being the very same.