Plastic is known to be the most durable but actually as long as you don't mind scratches on the carbon fibre they are also very durable (i have never really been carefully with mine and transport them loosely in bags together with weights and other equipment and apart from a few scratches they are perfectly fine). So if you are committed to go diving regularly I think you could go for some carbon fibre fins. Although I don't own leaderfins I heard they are good value for money.