I've used both for many years. Very similar staining characteristics. I prefer rollo (in trays or rotary) due to shorter development times and less base fog on films like the older HP5+. I only use PMK if I shoot a contrasty film like FP4 in contrasty lighting situations - i.e. not very often. I shoot HP5+ when the light is hard and FP4+ when the light is soft. BTW, my negs are intended for pt/pd/gum printing. I did some brief tests with Pyrocat HD a few years back and decided I liked the Rollo results better. If it ain't broke...