Sheet masks are saturated in liquid called an "essence". The essence is usually very high in emollients and humectants which bid water to the skin. Koreans are obsessed with dewy looking skin and the humectants are vital in order to give you true dewy, plump, hydrated skin. The sheet masks that we stock are then further packed with various botanicals and high performance ingredients that whiten, brighten and nourish in order to give your skin a variety of benefits. Because all our sheet masks contain brightening, hydrating and nutrient rich botanicals and no oil, they can be used on all skin types.
Clay masks are specifically designed for skin that is prone to congestion. Clay masks deep clean and refine pores. Clay masks are usually only suitable for congestion prone skin, enlarged pores and acne. Individuals that struggle with dry skin should avoid Clay masks completely unless the formulation includes carrier oils which may reduce excessive skin dryness.
So the answer is clearly that neither type of mask is superior to the other. It completely depends on your skin type and the type of result you are looking for. You could even combine both masks (I.e. Use a Clay mask and a sheet mask after for seriously amazing results) if your skin type allows for it.