I think they are about the same in the effect they would have on the bottom of a board.... but for more options (especially with the transitions from the up to flat to down rails) then Trex Deck (or similar composite material) is a better choice.
I can’t remember which video it was, but there was a clip of a rider hitting a PVC tube slider which proceeded to shatter throwing PVC splinters at his face.. It was bloody and very close to hitting his eye..