I should note that both ZBrushCore and Blender are not really CAD programs. While they provide the ability to create 3D geometry, they take a mesh-based approach, rather than one based constructive solid geometry. When it comes to 3D printing this is fine, but when it comes to other CAM-based operations this is usually insufficient. I wouldn’t recommend either of these for designing actual parts with reliable dimensions.
Out of the actual CAD options, I have experience with FreeCAD and Fusion 360. The former is, as it says, free, but that does come with an often awkward approach and learning curve. Fusion 360 is commercial, but is personally what I’ve settled on. It provides a comprehensive suite of functionality with a much nicer learning curve than FreeCAD.