sand is awesome. poo sits on the top, easily siphoned off without disturbing the sand. uneaten food sits on the top and will get consumed.
with gravel, uneaten food falls out of reach of the fish and decomposes. when i gravel vacc'd my tank after putting an algae wafer in the amount of detritus that came out of the gravel was truly disgusting. by comparison sand is very clean, you just won't keep it spotless because you see the poo sitting on it. usually the actions of the fish kick it to the side and it sits around the edges of rocks and ornaments where it's less noticeable (i have plenty of bottom feeders).
with gravel, uneaten food falls out of reach of the fish and decomposes. when i gravel vacc'd my tank after putting an algae wafer in the amount of detritus that came out of the gravel was truly disgusting. by comparison sand is very clean, you just won't keep it spotless because you see the poo sitting on it. usually the actions of the fish kick it to the side and it sits around the edges of rocks and ornaments where it's less noticeable (i have plenty of bottom feeders).