Features & how you draw
Does it support 3D, simulations, etc?
What features do you require for your project? This is a more important consideration than what features a particular program supplies.
Each program in our roundup has been designed to meet a specific need. LibreCAD is designed especially to make drawings on paper, or for reference. It has no 3D capabilities, while OpenSCAD can be used to make very complicated shapes and even 3D bar graphs, at the cost of a steep learning curve. Many of the drawbacks of using a scripting language are balanced by the plethora of scripts shared on different websites. For designing or even reverse engineering a piece for some old equipment you have, it may be easier to use the sketch mode and set the measured dimensions, but if you are creating a new unique work, using scripting can be very powerful.
LibreCAD has many libraries available from install, things like electrical and power drawings, but only one nut. It is however really easy to make your own library, just draw your parts around the origin, save them as a DXF and point settings to that directory. You can use the same directory as a templates library in QCAD.
QCAD is full of help for working on different shapes and mechanical pieces, making it easy to create a drawing, but without 3D capabilities you will need separate modelling software for finished 3D-printer work.
FreeCAD is full of features for both creating sketches and for transforming them into 3D shapes. Do some exploring and you can find spiral, helix modules and more. There are also mechanical analysis functions such as Finite Element Method (although this requires compiling the correct module), which can be useful. After all, before 3D printing you want to be sure that your piece will not easily break. FreeCAD ’s range of features make it the most complete of the bunch.
Solvespace has fewer features but is easier to get started with and exports to DXF, STEP, STL, PDF and other formats. Getting started faster may well be worth it even if you need to move on to a more complex program later.
OpenSCAD can take you far after your initial trial-by-fire. Getting used to the programming of shapes takes some doing but if you can already make simple scripts you should learn fast. Usefully, there are extensions for vi, Emacs and Atom, so you don’t need to edit in OpenSCAD itself.