I have had experience with all 3. If working drawings is your primary focus, stay away from Chief Architect which has more of a strength in interior renderings.
Both Softplan and Envisioneer are better at drawings and I have found and are pretty equal in quality and speed of production. Envisioneer is easier to use by far and has better compatability with AutoCAD files as it supports blocks, attributes, ACAD hatch patterns, dimension styles and layers where Softplan tends to reduce DWG files to lines and explodes just about everything. However Softplan gives more information in creating cross sections and is very reputable in producing drawings but is tougher to learn. Both products have quality forum and technical support and support is free of charge. I found Softplan to be overpriced for a comparable product so ended up with Envisioneer as my choice.