Whats the best bearded dragon substrate?

Shes about 16 inches long, so i'm not really worried about her doing something stupid. I've been using millet, but its just so hard to clean and needs to constantly be replaced. I want to use sand, but from what i've heard i'm a little worried about impaction. I've never seen her "eat" the millet, so I don't really think she would eat the sand. I'm still a little worried about it though. Whats the best substrate to use that still looks good?