Kaedeb, welcome to Tropical Fish Keeping forum.:cheers:
To your question, as has been mentioned by others, the needs of the fish intended for the tank should determine the substrate. Plants for the most part will manage in almost any substrate, but sand or fine gravel is the usual. As one who has experimented with so-called "enriched" plant substrates, I wouldn't waste the money.
If you have substrate fish like corys, sand is definitely better. A fine gravel can be useful if you want to set up a Central American stream, or an Indian (South Asian) stream. I rather like the look of sand, and now have this in 6 of my 7 tanks.
Byron.