What's your definition of "best"? Some people like/prefer the factory phenolic pistons, but I'm not one of them and I tend to purchase the units with steel pistons, as I've had better luck with them. That said, they're all remanufactured AFAIK at this point, but different remanufacturers vary in terms of quality and finish. Some are coated for corrosion resistance (Cardone) or zinc plated (Centric), some are left bare.