When I first moved to the farm, I put a stonedust floor down in all of my stalls. I didn't put mats down because of the expense. I wish I had, because even though the floor got almost as hard as a rock, the horses eventually dug it up (not to mention the stallion's pee hole!) and I ended up completely redoing it this past fall. Cost me as much as the mats would have, not to mention all the work (I did everything by hand).
So this fall I put the money into rubber mats which went over the limestone screenings. It is working great, saves a LOT of bedding, and the horses seem very comfortable on it.
The key is really packing it well and giving it time to "settle" before you put the mats down or put a horse on it. I packed it by hand (what a job!). I would recommend renting a packer.
Edited to add:
Oh, we do have stalls with concrete floor and rubber mats. I like the limestone stalls much better. The wet has no place to go in the concrete stalls, and it seems to take a lot more bedding to keep the stall dry and fresh than the stalls with limestone under the mats.