I have tried a lot of different PBT, like IMSTO thick, KBC and Vortex (sold by qtan and feng). I have also tried both regular ABS (this is what I used most of my life) and ABS doubleshot.
To me personally, I thought the biggest difference in how they feel was because of their profile. Cherry profile keys are lower in height than the typical OEM profiles. Both IMSTO thick and ABS doubleshots have this lowered profile. A lot of people prefer it, I do not mind either but actually feel a little more comfortable using regular OEM. That could just be because I am more used to the higher profile though.
The second thing that stood out when using the different keycaps was the roughness or grainyness of the surface. Though this might have to do more with the production process than the actual material they are made out of. That said, the PBT keys available tend to have a more textured surface area. Though the Imsto thick PBT felt a little smoother. This does not mean that they have more grip though. I personally found that the smooth ABS keycaps felt less slippery than most PBT keycaps I tried. The flat, smooth surface seems to have actually more resistance when pressing a keycap. But perhaps this is just different depending on how sweaty your hands are. I have very dry hands, and ABS feels grippy without ever becoming slippery.
The last thing that I felt that made a difference are both the thickness of the keycap material and the material they are made out of. I use PBT most of the time at home, but have ABS at work. My verdict? Personally? Once you are used to them they are both pretty much fine. I have no real preference. ABS feels a little softer and more forgiving when bottoming out. If I would not bottom out on a lot of my keystrokes I would not even be able to tell the difference. To me, I like this about the ABS. The plastick is not as hard it seems, and you feel this. PBT is harder and feels more "snappy" almost. This also feels good in its own way, but personally I do not think it feels objectively superior. The great benefit from PBT to me is that it resist shine much longer, and lighter colors will not change due to exposure to the sun. I never minded shiny keys in the sense that they became uncomfortable to use, but it does look kind icky, as does the discoloration that can happen over time with ABS.
Would any of these differences be enough to make me spend over 50 bucks on a set of keycaps? Personally no (yet I did, many times). The main reason I would buy different sets is for customization and changing the look of the keyboard.
