I have to say, I like gravel. However, sand is good for growing plants. On the downside, it really clouds up your tank for like the first week or so. Sand does tend to give your tank a smooth looking bottom though Gravel tends (or so it seems) to add more texture. However, it is just a touch harder to grow plants (my experience) because of all the gaps. I really think its all how you want your tank to look.