What CAD software is best for Automotive design and manufacturing?
It depends on what part of the automotive assembly you are working on and also if you willing to purchase a software as an individual, or a company.
For outer shape design: Rhinoceros 3D is the best (Renault, CanAm... uses it) in my opinion.
For the mechanical part: Inventor, Solidworks. Catia. Unigraphics, Pro Engineer.... The problem is that these softwares can do far more than you ever need, but still you will pay their prices as an individual.
I personally use Rhinoceros because it has an endless numbers of plug-ins even for "automotive" designs (I mean mechanical engineering design) and it is very easy to use. Rhinoceros is one of the most effordable software for individual purchase for a free-lancer.
You can also make the firs steps of doing concepts with FreeCad + Z88 AURORA for finit element analysis, both an open source CAD initiative.
I hope it will help.