They are very similar morphs, but they are definitely different. Black pastels have very very intense blacks and really dark golds, whereas the cinnamons tend to be a bit more on the brown side. As supers, the black pastels are pretty much jet black whereas the cinnamon will be very dark brown, and they'll brown out more with age.

Personally I'm more fond of black pastels because of their intense coloring, but that's just a matter of taste.

Another small thing I noticed is that with super black pastels you don't see as much "duckbilling" as you do with the super cinnamons. Correct me if I'm wrong, just a personal observation.