I prefer Solidworks over Autocad.
Solidworks - A Windows application with a 3D solid design for a final product.
Autocad - A DOS application converted to Windows, with a 2d design, and 3d as a added on much later in development.
I have 7 years experience in Autocad, and I found it somewhat easy to transfer to SW. Solidworks usually will output a good STL for use on my companies Connex 350 Resin Multi-Material 3d Printer. but be warned, all CAD programs have their issues.
Both taking classes on how to use the software, and having a copy to "play with" are critical to figuring how best to use the software. Community College classes qualify you for the %90 percent or so student discount. Also in my job my designs are propitiatory, so I can can't post them online, but if you if you can post it, there are many people who will help you though the design challenges.
Screw threads are particularity tricky as SW treats them as a cosmetic feature, and you have to make them by hand. The book "Machinery's Handbook" is a good resource.
lvdata