I have gravel but I wish I had sand because its much easier to keep clean. But also if you have sand, you have to stir it up every once in a while or keep little critters that will do it for you, or else toxic gasses can build up in it. But that isn't such a big deal, just buy some sand digging fish of some kind. Another upside to gravel is plants seem to stay anchored better.
And like I said, easier to clean. To clean my gravel, I have to take the vac and stick it down in there every couple inches. But with sand you just wave it over the top to suck up the icky stuff. (sorry that was kind of long lol)
"A fish with his mouth closed never gets caught" -mob quote