Andy,
It depends where you are travelling to and from. Best roads for me are out the back and onwards to Loch Lomond (Sorry useless with road numbers). Also the roads around Doune and out towards Hi Soobs neck of the woods.
Going back towards Edinburgh, come off the motorway at Linlithgow and take the road that runs parralel with the motorway toward South Queensferry etc, providing there isn't too much traffic it can be a good laugh.
Ian