There are several competing programs, like 3dsMax, Maya, Cinema 4d, SoftImage, or Blender. Of those, Blender is free, but In my estimation, Cinema 4d is the easiest to learn (and what I use the most. I also use 3dsMax, but I hate that one, really). The non-free programs are quite expensive though, and they are made primarily for visual quality (photorealistic lighting, effects and materials), not millimetre accuracy. For that you need a CAD program, like Autocad. Expensive as well, though, and not easy to get into.