Any of them will work, the difference is in ease of design/fabrication, and adjustment. With #2, those "washers" are shims which are used to set the bearing pre-load, so when you install the shaft, you can just tighten up the nut and get to work. With the other two designs, the nut torque determines the bearing preload, so assembly is more critical if you want to avoid backlash (if the nut is too loose) or rapid bearing failure (if the nut is too tight). Personally, I'd go with #2. Bearing shims are available from McMaster-Carr.