Memory foam, cotton, or diatomite stone — which type of bath mat is best?

It depends on use case. Cotton mats are the easiest to launder and the most forgiving in family bathrooms; memory foam is the most comfortable underfoot but eventually compresses and the rubber backing degrades in the wash; diatomite stone dries the fastest and resists odor but is hard, breakable, and can't be tossed in the laundry. Specialist r/BuyItForLife threads repeatedly note that the 'right' choice is usually a combination — a soft mat outside the tub and a non-slip surface inside it.