The slippery one is probably ABS, the other is probably PBT. PBT is superior for a number of reasons. First, they usually just feel better. Second, over time/use ABS caps tend to get shiny. This isn't reversible and makes the caps look pretty awful.
Searching for PBT is pretty much all you need, although that GK64 doesn't have the most common of layouts, although it is widely supported. Good luck!