В целом Cocamidopropyl betaine "нежнее". Но на него при длительном использовании често возникает аллергия или контактный дерматит. Вот по английски из энциклопедии. Cocamidopropyl betaine is a synthetic surfactant; it has been associated with irritation and allergic contact dermatitis, reactions that could be due to the ingredient itself or to impurities present in it, such as 3-dimethylaminopropylamine