One of the characteristics is two of them are one word.
Welcome n00b!
Short version, compared to MM
A-Pig - fatter, grindier, more compressed, gainer, bit looser, crunchier, more mids, similar bass, less treble.
NB - Much fatter, sweeter high end, slightly tailed off, looser (also than the pig) bigger sound, much more mids, richer, more organic (than the pig as well), lush cleans, not quite as hot or compressed.
PK - Tighter, more attack, similar bass, less low mids, more mids-mids and much more high mids, less treble, slightly hotter, more percussive, fatter, bigger, grindier.
All of them clean up and roll back better than the MM, imo. Order of goodness for this (again, imo):
WP
PK
NB
With quite a big jump in quality of lower gain and cleaner sounds (especially vol roll off - the MM is quite unusual for a BK in that its not really happy unless its going full tilt) to the WP, then that and the PK are pretty close (I could see how someone would disagree with that order) then the NB is way out front in versatility/volume controllability.
