Stump-grinders can leave part of the stump in the ground--it will rot and sink. Ripping them out is best, as Dave says. Another good fill is called "QP" for quarry product. It's like dirty gravel but packs really hard and has a VERY high friction coefficient--that means it doesn't move once it's packed down. Drains as well as gravel too, and it's usually a LOT cheaper. New developments (like the one behind us) frequently have it because they have to break up and grind lots of boulders, especially if it's very rocky soil--as ours is.