The difference between urethane and neoprene is the density of the materials. Both will have a cushioning effect. That is why there is a buffer there. Neoprene has nitrogen bubbles in it, so it has more give and will compress more than urethane. Urethane is more dense so it can be thinner but still protect the receiver from the impact of the bolt. I have used both. I have not noticed the difference in the recoil impact. Personally I think the condition of the recoil spring is more important than buffer materials. Ultimately the spring needs to be strong enough to slow the rearward travel of the bolt, stop it, and send the bolt back into battery with the next round. It needs to be weak enough to allow the bolt full travel of the bolt stroke but not impact the buffer for best performance. But the recoil spring is a wear item. Over time the spring looses its strength. How old is the spring in your gun? A new recoil spring will have an initial "set", where the spring will shrink in length once broken in. That would be the best time to "tune" the recoil spring. If the recoil spring is too strong, the gun will short stroke. There is a spot where the bolt will come back far enough to eject the spent casing and strip a new round, but not far enough back to catch on the sear. The gun will run like this, even if you let go of the trigger, until the mag is empty.
That brings up another issue of "tuning" the gun is the power of the ammo. Sorry I don't have time to get into that right now.
Scott