I started with KC and switched to HKN. I switched because I was interested in mouse broadcasting that KC did not support very well at the time. I also liked the idea that once I made a good script for myself it was easy to modify for new groups, or even computer changes. I travel a lot and use a work laptop and a personal slimline pc with a hotel tv as a monitor usually. The ability to use several machines without buying a key or dealing with transfers everytime I got a new laptop was a serious benefit as well.

Scripting is a personal hobby of mine, which also made HKN attractive, but for a purely personal reason, so I would have to say it's a reason I stay with HKN but not a reason I left KC.

Anything free is nice, but KC, IS/ISBoxer, and GCP all provide a product worth way more than you pay, so while key requirements were a consideration the cost was not.