The "best" kaolinite for any application depends on what it's being used for. Some factors influencing the quality include:
Purity: High-quality kaolinites have fewer impurities, such as iron oxides, titanium oxides, or organic materials, which can affect color, plasticity, and firing properties.
Particle size: Finer particles improve surface smoothness and strength in ceramics and paper coating applications.
Whiteness: For paper, ceramics, and paints, high whiteness is desirable, which requires low iron and titanium content.