Unless you're looking for whitewall shots, check out my
Ti-PD/PD-S/PD-S-Mizer Shootout.
For the money, my particular PD-S has a slight edge in total output, throw, and tint, while the XR19-C has a slight edge in spill. The differences are so small that, from a purely functional standpoint, it's a draw. But the LED lottery still lives, so if I had a different PD-S and/or a different XR-19C, it might tip the other way.
To me, the primary difference between the two is whether someone has a preference for the piston or a clicky. In real use, that's the only difference that can be easily detected, IMO.
For me, I tend to hold them like I used to hold a cigarette. Because of that, I lean towards the C-pak. The narrower body is easier to keep a good grip with when held between my first and second fingers with my thumb on the switch. I find it more likely that I will drop the PD-S in this grip. So the XR19-C is used around the house more. But...
Which light do I carry in my pocket? The PD-S. Go figure....
So even though I've had both for a couple of months, I still haven't really formed a preference. :touche: