As mentioned, it's more personal choice. Lighter substrates seem to mute the colors of the fish as mentioned by drobbyb. I prefew black substrate as it really brings out the color of the fish. Both will be equally clean once you wash them good before adding them to the tank. And they will probably be about the same tint (dark or light). As far a what type playsand, they are all pretty much the same. You can get it in a bag at most all home improvement stores (not sure what country you're in).