I don't think there's either is "better" unless you have Cories where sand is preferred because it's gentler on their barbels. It's more a preference.
I have and prefer sand over gravel because all the gunk stays on top of the substrate so it's easier to vacuum. Just hover the vacuum/tube over the sand; don't put down in it like you do with gravel.
I find sand easier to plant and my plants seem to stay anchored better than when I had gravel. I don't know if it's technically true, but it seems sand wouldn't "bruise" plants like gravel does.
Besides the above, I simply prefer it because, to me, it look more natural.