I have 2 favorite 'gravels'..
Onyx Sand and Flourite (not Red Flourite) are made by SeaChem and mainly used along with live plants. I like the small grains of the Onyx. Large gravel makes the aquarium appear smaller, where sand, or smaller gravel gives the tank a larger look. I think the darker gravels look better.
While on this subject, I think it looks much better to have sloping gravel rather than level. Having gravel deeper in the back of the tank gives a better depth of field --- it makes the aquarium appear larger, which is a good effect. In live planted tanks, having deep gravel in the back is good since the taller plants are generally placed in the back. The larger plants normally have more and longer roots and need deeper gravel/substrate.