Which one should be recommended for potato?

Sulphate of Potash is the one that is recommended for potatoes. sulphate of potash contains the most efficient balance of nutrients to optimize potato yields, quality and storability.
Potash is an essential nutrient for all plants and has a major effect on the yield and quality of potatoes as well as the general health and vigour of the crop. It also helps in regulating the amount of water in the plant.