It's a matter of personal preference really, and also what sort of fish you want to get.
Live plants will grow equally well in sand or gravel. The roots will grow well and feed on all the muck produced by the fish etc.
Sand looks great I think. I started with sand but had to change it because I had bought coral sand, so my pH just shot through the roof. If going for sand, make sure you dont make the same mistake
. I took it out and replaced it with gravel.
The only potential drawback with sand is that you can get pockets of gas building up in it which can cause problems for your fish. You get round this by stirring the sand when you do the weekly water change. You clean it in a different way to gravel - just hoover poo, food etc off the surface by holding the gravel vac above the surface.
Gravel comes in all coours and sizes. You need to get a gravel that is smooth (pea gravel is best I think) so that any bottomdwellers dont hurt their barbels on it. It's easy to maintain with the weekly cleaning regime - dig the gravel vac into it and suck all the muck out of it.
That's basically the difference between the two - the choice is yours!