As an equine vet, I visit a lot of different horse barns and see many different kinds of stall flooring options. There are two basic options for stall flooring, those impervious to liquids and those porous. Porous floors are inexpensive, and they include topsoil, clay, sand, and some road base mixes. In general, these floors work well especially if they are in a barn that is on high ground so the chance of water getting in the stable is low. They are also easy on the horses because they are relatively soft and generally aren’t slippery. 

The major concern about porous stall floors is they are impossible to sterilize completely in case of a contagious disease. Also, they will retain odor and will require removal of a portion of the base along with the bedding to get rid of all the waste every few days. So even though the initial cost of porous stalls is less, in the long run they require much more labor and more bedding materials.  The most common impervious stall floors are made with concrete. Concrete is excellent and can be completely sterilized. Although initially expensive, it may pay for itself in the long run. If you use concrete, in my opinion you need to use thick solid rubber mats as cushion. Shavings can be used on top of the solid rubber mats and this works very well and is comfortable for the horses. Since you are using rubber mats, you can make the concrete surface slick because traction is not a concern on the concrete itself. This makes it easier to remove the mats and completely strip the stall when necessary. There are many options for stall and barn flooring and spending some more money initially may pay off in the future.