Quite simply, whetstones are "best" for Japanese chef knives. The sharpening steel is used after every use to remove the oxidation and other buildup from the blade. It is then further refined with the whetstone on a regular basis (2-4 weeks depending on how much you cook) to keep it finely honed and ready for use. The whetstone not only causes more wear to your knife, but with time will take out some of its hardness as well. I would not recommend using any kind of stone or steel if you have a fine forged Japanese, French or German knife because these kinds of knives need very little maintenance and instead should be professionally sharpened periodically by a professional.