If he is a baby or juvie, having him on sand is very risky; it often causes impaction of the intestines, which is more often than not fatal. I have heard that adults deal with sand better.

From what I have read (I don't actually own a Beardie yet, but I've been doing studious research for months in preparation), I am going with tiles. If one is pooped upon, you can take it out, wash it, and put it back. Easy to clean, and it also wears down their nails so you don't have to clip them.