I've used wood from the back yard that I've cleaned up, driftwood, and the plastic/pvc decorations. The problem with wood is that if it gets pooped or peed on it can be difficult to clean up as the mess soaks into it. Yuck!
Plastic ones clean up easily, but you have to make sure to get decorations that are safe for reptiles. Sometimes people make the mistake of using plastic or stone decorations that are designed for acquariums and have openings so that your BP can just squeeze himself into them... and not get back out.