What do you want to use it for? I have some leaning up again my front glass acting as caves, another piece between two rocks as a table/USD cat hiding place, and third large wild piece that is the centerpiece rock of my tank
like Jaysn said it all depends on what you want to do with it. some people stack it up to wake a wall background. some people stack it up a few of them to make some caves. some people use them as a place for angels to breed. others i have seen use to to grow plants on like riccia. until you know what you want to do i dont think anyone can help you.