Sand: My understanding is sand will not
usually pose an impaction problem for beardies over about 14", as they can pass the particles okay. Smaller dragons are at greater risk. Sand also looks nice. However, sand is not preferred by many owners and breeders as it is more difficult to ensure all fecal matter is removed from it than other substrates, and it can be somewhat dusty for the dragon. Also, even if they can pass the sand, why make them pass the grains through their system if you can avoid it? And if anything goes amiss with husbandry and the dragon gets dehydrated or underheated, the sand poses an increased risk of impaction. There are many reasons well-kept pet dragons have much longer average lifespans than wild dragons exposed to many more risk factors.
Calcium Sand: Calcium sand can be digested, and therefore poses risk of impaction. However, some feel there is such a thing as too much calcium for a dragon's liver/kidneys. Also, the sand will also hold bacteria and parasites from fecal as with regular sand.
Paper Products: Many people use paper towels or newspaper. These are cheap and easy to replace, and won't hold bacteria/parasites from fecal like sand if replaced often enough. They don't look as aesthetically pleasing as some other options though.
Reptile carpet/artificial grass: In my experience reptile carpet is a decent option, though it can be on the pricier side and does tend to absorb feces. They can be washed, but to ensure bacteria/parasites aren't lingering in the fibers, it's best to replace it which gets costly. The looped fibers can also snag dragons' toes/nails, possibly hurting them. Artificial grass/turf has similar issues with microorganisms, but would be less likely to snag.
Walnut shells/other shells: The consensus is that you should NEVER use walnut shells, as they are very likely to be ingested and cause impaction.
Tile/Slate: I just switched to this for my new setup. It's a bit of a hassle to make sure it's cut to size (Lowe's does it for free), but once it's in place it's very easy to keep clean, and can look very nice. It also helps file down their nails. It can be removed for cleaning, or left in place. My tiles are very large (just 2 fill the 40 gallon viv), so I plan to leave it in place to clean unless fecal gets under it somehow. The tile is on a layer of paper towel to protect the glass. Here's a pic: