If you are a beginner and want one functional and economical stone, buy the synthetic, comfortable and durable Silicar Rotmarke.
A scythe finished with a finer grit cuts with less force. However, when the scythe is too blunt, the fine stone is not able to remove enough material to create a quality edge. In this case it would be ideal to use coarser stone first and follow with a finer stone to finish the edge. In practice, however, this is usually not done. When the scythe stops cutting easily using a finer stone, people usually switch to using a coarser one. If even with a coarser one it does not cut well enough, it is necessary to peen the scythe.
If you appreciate the pleasant feeling of the touch and the sound when honing, choose a combination of two natural stones. Coarser French Saurat and finer Slovak Rozsutec. These are traditional stones with a long history and are now popular all over the world. Effective use of the Rozsutec requires a really fine peened blade.
If you have a very dull scythe that you can't peen for some reason or if you use a peening jig, a coarse carborundum stone in combination with synthetic Silicar Rotmarke or natural La Saurat will be needed. Use a carborundum sharpening stone to create an edge (grind the blade from both sides until the sharpened surfaces meet and form an edge) and then hone with a finer Silicar Rotmarke or La Saurat.