Cast-iron woks are generally the best as they conduct heat more evenly and quickly than any other material, but they do need more careful treatment and seasoning with oil and salt. Traditional woks are round-bottomed and need to sit properly over the heat without wobbling. As most gas rings are set with metal prongs, these provide a steadier base than electric rings set flush with the surface. But you can now buy slightly flat-bottomed woks that can be used on any stove, and also round metal wok-stands that hold woks steady above the rings of both gas and electric hotplates.