I like the black, but it depends on the fish you keep. Most fish show their best colors on a dark backround. However, I've found that Calvus will sometimes develop darker spots on dark substrate. I think they look best with bright white spots on the jet black body.
I used crushed coral, white pool filter sand, and black sand from the LFS all mixed together. The sand looks great and the crushed coral works as a buffer. As long as you use dark rocks and or plants, your fish should show good color. When I finally rescape, I think I'm going to use brown substrate.
Both the lakes look alot alike, and like Pittbull said, it's mostly large boulders with some light colored sandy spots. Most of the fish we keep in the hobby would be hanging around the boulders, so they really wouldn't care much what the substrate looks like.