These are just my personal observations:
Mothers is the glossiest out of the lot, but it also has the shortest lifespan. It also does not release dirt the quickest with inital rinsing. It does, however also offer the best hiding ability when dealing with light scratches that are bound to occur eventually when washing or dry the car. The best on reds and dark colors, but does mute metallics a bit more. than the other 2. Worst protection against enviromental and industrial fallouts) Most available at OTC stores and online
845 is the middleground in terms of gloss, durability, and releaseing of initial dirt during the rinse. It hides ok, but not as good as Mothers. Slightly mutes metallics, but leaves a nice looking finish that has some pop. Decent protection against enviromental fallout- better protection against industrial fallout. Primarily available online, but some select OTC stores may carry it
1000p had better anti-static properties and rinses very clean before even doing a wash, but is very sterile looking; whatever the paint looks like after you polish and glaxe is pretty much what it will look like after 1000p. It also happened to be the slickest feeling of the 3, which probably explains why it releases loose dirt and dust so well. Slightly longer durablilty than 845, but not by much. Hiding of light scratches is the worst of the 3, however it can improve with multiple applications (can layered same day, but 2-3 applications is pretty much the limit for the most part). Provides the best protection against both enviromental and industrial fallout.
Available online only.