i agree with the sand bit but it is important to have a few diffrent particle sizes so it doesnt compact. it is also supposed to be better for the creatures crawling around in it. i assume that your talking about a dsb.
It is said by wiser men than I that Aragonite sand will begin to buffer the water as the PH drops below 8.3 whereas crushed coral does not begin to have and effect until 7 and change.
But perhaps this is irrelevant if you are running kalk reactor or drip.
I prefer the sp. seafloor grade sand, from carib-sea. I have had excellent results this way with very little detritus accumulation. detritus will build up in any bed on any grain size the trick is to keep high enough flow in the tank to keep most of it suspended. Of corse the larger the grain the faster the detritus will build up.