It all depends on what you want. I love sand, but an under gravel filter wouldnt work with sand. If you want gravel, go to a fish store and see what options are available. If you plan on doing plans then its nice but not required to have a special substrate for plants. If you want africian cichlids, its nice to have crushed coral (I believe thats what it is) to raise the PH. You can do whatever you want. My favorite looks are black gravel, or sand, but you can do blue rocks if you want to.