Knowing the activity levels tells us if software is viable long-term.
In order to choose the correct package, you need to decide what the goal of your project is and from there choose whether you are going to use a 3D-printer, CNC router or other more traditional methods to build it. You also need to know how well supported the package will be and what new features may be due in the near future. If you are interested in contributing code it is also useful to see how active the developer community is.
To get a true sense of the situation we’ll look at the development pages of each package – usually GitHub.
LibreCAD has a version 3 on GitHub which seems promising, with the code divided neatly into three distinct parts that show good organisation. With 47 contributors in general and seven dedicated to version 3, this project may improve quickly. 3D support does not seem to be in their plans, however.
SolveSpace is still in development but with very few contributors. Tickets are still handled fairly quickly so there is hope.
FreeCAD is still in beta, 0.17, but is already fully usable and has many features, such as mesh handling and FEM support. The constraint handling in the sketcher needs some improvement, finding the final constraint can be tedious at times.
That said, the project has a strong set of developers and many sub projects, if these are well coordinated then there is a bright future ahead. Python is the scripting language of choice.
OpenSCAD has a big active community developing scripts but the program seems to be kept maintained only. QCADPro does not boast any upcoming improvements but the community edition is available on GitHub and has seven contributors (but only one seems active). If you really like this program, start contributing.