I've used pyro PMK and Xtol. PMK pyro renders snow very nicely. XTOL is great for shadow detail. I don't think one is better than the other. It all depends on the subject matter you're shooting. I terms of safety, XTOL is the winner. Just buy both developers and do some testing. Luckily, both developers keep well. I mix my Pyro PMK right before I use it. The weird part of using pyro PMK is after fixing, you dunk the film back into the developer.