The finer the sand in the coop the better, from my experience. It's easier to sift out the droppings from fine sand than it is from somewhat gravely sand. I use sand, myself, and I love that it's not only easy for me to clean out, but gives the girls somewhere to dustbathe when it's rainy out. The sifted out droppings can go into the compost and the older sand can go right out into the chicken yard to help keep down any muddiness. 
