Diamond stones (aka diamond files) are the best option to maintain ski and snowboard edges due to their ability to cut and polish the edge for a smoother, sharp edge. Ease of use, can cut or polish in any direction, long life, and very forgiving since they remove less metal than a file and, diamonds are a must have for any tuner.
The heart of the diamond 'quiver' is the 200 and 400 grit diamonds for sharpening and polishing. A 100 grit diamond can be used for establishing edge geometry versus a fine file, while the finer grits can provide that extra level of smoothness for the more demanding. The flexible backings and unique moon shaped pattern of the Diaface Moonflexes are very popular. A rigid, durable backed, Tools4Boards Hone Diamond stone offers desirable feel and feedback for some and replaceable diamond strips.