I use aspen, but I put lots of hay on top so the aspen never touches my rabbits. Hay is pretty cheap if you buy it by the bale. The reason I like aspen is because it makes good mulch around my plants (especially after it has been fertalized!) and I don't have to fill up my garbage can. I use the old hay for around my strawberry plants. I also use hay for bedding, and when it gets old, I replace it with fresh hay and use the old bedding hay for the litter boxes. I also cover the bottom of the litter boxes with newspaper because I think it helps the litter stay dryer longer.