The best driftwood I have found has been from a local trout stream. The current is swift, by Michigan standards and the pieces I choose have a nice sanded look. I have also collected some from the Lake Michigan shoreline but there is a lot of competition there because people like it for landscaping.
I treat it by boiling it for a while and scrubbing with a stiff brush. Some of it has to be weighted down which I have done by drilling slate and running an aluminum screw into the wood.