Ill vote Kelbly as well. I dont own either but ive felt both and shot both. The stiller was good, but i prefered the Kelbly. I doubt youd be dissapointed with either though.
The Kelbly had the TG ejection, i thought that was cool, they just upgraded he bolt stop too (its stronger. Not hat its needed but why not) and it felt faster than the Stiller. I cant really explain why, maybe it was worn in better. The stiller was smooth but not as smooth