We use AutoCad, why, well we both have engineering background for architecture mostly and mechanical design, we are fanatical on precision and detail because we were both in the field. AutoCAD is mostly engineering software and we both love it. The acurracy is amazing. And we both learned AutoCAD around 16 years ago, once you learn a software it can be real hard to switch to other 3D modeling software, the difference in terminology can put you in a tale spin. We have breifly tried others and always return to AutoCAD. Sharen