Well it depends for what reptile, really. Out of all the substrates I use best, I do have a preference for crushed walnut (i think only zilla makes it) substrate in my beardie tanks. I like it, I don't know what it is exactly. I've had it for years and I mean beardies seem to like it, it looks nice, and I don't have problems cleaning. And for being particle, it doesn't weight as others do.
by the way I wasn't able to actually VOTE because the poll is closed I believe.