I just counted the number of projections available in PtAssembler and came up with 25. Some of those 25 are probably just there just to say that it's there and are not actually useful. Plus, there are probably a bunch that are so close to each other that in the real world it doesn't matter which one you use.
So let's say that there are ~10 usefully different projections. a) which ones are they? b) in what circumstances is one clearly better to use?