Coarse grain sand. Fine grain shows more mess and is harder to clean. Gravel conceals the mess so you often don't end up cleaning thoroughly enough. Just my (very recent!) experience.
Edited to add: most of my plants are java ferns and anubias, so they are attached to wood, but my crypts are planted in flourite in terracotta pots pushed into the sand. That way I can move them around without damaging them, and they get good soil and root tabs.