When comparing QCad vs OpenSCAD, the Slant community recommends OpenSCAD for most people. In the question“What are the best open source CAD tools?” OpenSCAD is ranked 3rd while QCad is ranked 4th. The most important reason people chose OpenSCAD is:
Because the 3D-objects will be programmed. You define basic geometric objects, scale, rotate or move them, create unions, intersections, hulls, differences, ...
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Powerful and has many features
If you learned AutoCad, the tools are very similar.
Pro Ideal for programmers
Because the 3D-objects will be programmed. You define basic geometric objects, scale, rotate or move them, create unions, intersections, hulls, differences, ...
Pro Text based description
Hence the resulting files can be easily stored/merged in version control systems.
Pro Parametric
Define some variables and use them in the code.
Pro Easy to use
Cons
Con Commands typed in aren't the same as Autocad
Con Is not available in the packages of (K)Ubuntu, unlike LibreCAD (a free/libre fork of QCAD)
Con No 3D like FreeCAD
Con Need to know scripting
Con No measurements from any area
Con SVG exports a single big shape
It should export one shape per object, so it would be re-usable in SVG tools.