When I put this question to a recording whizz some years ago, he suggested that the most reliable longlife recording medium was the late 19th/early 20th century cylinder. It was superior to the flat disc, in that the stylus moved at a constant speed in relation to the groove and all the information on a well-cared for cylinder could be retrieved a century after its manufacture, without serious loss. He had no views to offer about transferring CDs to cylinders, so I decided not to do it.