For me, the definitive work on developer components and developer operation is in a book called "The film developers Cookbook" Anchell - i always keep it at arms length. It explains all the different kinds of chemistries, what they do and why and gives formulas for practically anything. As good as the info is from this group - you can't do much better than that book to build a foundation of knowledge on which to add the subtleties gained here. PMK is a great developer - I have used it for years - I wouldn't recommend it for cute little film or MF that will get enlarged past 11x14" I have just begun to use Pyrocat HD = the grain is much smaller and there is less general stain. It is still not Microdol for the small formats. I have settled on 4 developers for my use:
120 and LF get Pyrocat HD and get used based on what I will print on and how much contrast expansion or contraction I need.
35mm and 120 that will get enlarged past 8x10 I use Microdol
Special films or anything push processed go into D76
For unknown exposure situations - i.e. antique cameras and guessing about odd varied lighting go into a split D23 soup that will just about make anything look good.
80% is pyro