I have never kept a gravel tank so cannot comment on gravel
Sand is a great substrate but like everything its not perfect, the negatives I would say is vaking up debris is a bit of an art compared to gravel.
In that you do the same as gravel but with just a hose no fancy end bit and you don't stick it in the sand its a fine art of hovering just above the surface of the sand sucking up the waste/debris.
Debris and waste does show up quite clearly unless you use the darker coloured sand.
You will inevitably loose some sand over a period of time doing this, in fact I have just topped up my sand substrate I do it about every 8 to 10 months.
The other major issue with sand is that if you have major currents in your tank it will move the sand substrate around and you will end up with a pile of sand in one corner, so you have to spend a while testing your flows getting things Wright.
But bottom dwellers like Loaches love sand substrate

It does look fantastic

I hope this helps.
Regards onebto.