As a 3d draftsmen myself, I am currently using Inventor for all my jobs, with other programs for rendering. I started with autocad but feel it really is much more useful for 2d modeling then 3d. In school I used soildworks and I think that may have been my favorite program. If you are going to be dealing mainly in 3d I would really look into inventor. The commands are so much more 3d oriented but still share similar traits with autocad since same manufacture.