I think before anyone answers this question, they would need to know what you are using right now, and how soon you want to move to the "latest and greatest." Are you using Land Desktop w/Civil Design? Have you been planning on buying Civil 3d, but you're just not sure which one? Civil 3D comes with Land Desktop "companion." It's full-blown Land Desktop, but it will use the same software license as Civil 3d. Civil Design Companion is the Civil Design add-on for Land Desktop. It does not add any functionality to Civil 3D. This allows Land users to be able to continue using the software they are comfortable while they migrate, as well as get some functionality that does not yet exist in Civil 3D. If you haven't used Land Desktop, and you don't know what Civil Design is, then you don't need it. If you have used it, and you are not planning on embracing Civil 3D overnight, than you will want it.