On my black car, I've topped AIO with Souveran, Klasse SG, NXT paste and S100. As a topper for AIO on black, these are my opinions:
-Souveran: Adds incredible wetness, depth, seems to darken the way the car looked, gloss of AIO still showed, awesome by any measure but only for about a month and a half.
-SG: wet, very glossy without turning silvery, still see the color of the car, super durability, looks very good for a longer period of time, doesn't hide swirls which can be a problem with black.
-NXT paste: looks very good but not in the same class as the 2 above, won't last as long (need to prep paint to last a couple of months, something I didn't do), helps hide swirls, a superior OTC product.
-S100: seems to be between Souveran and SG in most traits like gloss, wetness, depth but not as satisfying as either of them. It would be a toss up between S100 and NXT paste. Dulls the gloss of AIO and replaces it with its own version of gloss. Has a hint of "silveryness". Still an excellent product.
I tried Souveran on top of AIO/SG and I seem to prefer AIO/Souveran without the SG.