i prefer gravel! though there are a couple of different sands you can use that are good for discus, some will raise your ph ect..... just make sure the sand doesnt affect your water quality, ask your LFS where you can source some!
I use a product called eco complete in all my tanks. I had it in a 120 gallon tank with discus. Its black and sandy, yet has some gravel particles in it. It also buffers the Ph down to create an Amazon effect. Its about 20 bucks a bag, 20 lbs. Heres a link to the site where I got mine. Its very easy to clean and makes the discus colors coem out.