I was looking at an old Wrotniak E-500 review and he said that most of the time he set the sharpness at -2 to “allow for more freedom in image postprocessing”.
I leave mine at the default setting for JPGs but for critical work shoot RAW + JPG and then adjust the sharpness and other various settings in master2 to get best final effect. I fact I am almost always very pleased with the JPGs and usually only want to adjust the levels slightly, and possibly crop.
Perhaps I should have pointed out that in master2 the exposure sharpness setting is recorded in RAW and is used as the default, but all settings from -2 to +2 can be accessed if you want them. I am not sure if that is true of all RAW converters, and also the "best" setting may well vary depending upon which lens you are using. As it is possible to print test images using every setting you could experiment a bit to see which suited you best.