What are the differences between Studio 2 and LDcad when working with Technic and EV3?
Please note that I think that software preference can very often be based on many factors that are difficult to enumerate and sometimes even more difficult to express. That said, I think there are a few important differences between the two specific pieces of software that you referenced that could be useful for answering your question. (Also note that my impression of LDCad is based on a much more limited experience as I am more often a Bricklink Studio user.)
Interface
Bricklink Studio's interface is more similar to your previous software, LDD, in that by default it has &quot;part snapping&quot; enabled. The default camera viewport behavior is also similar in that clicking and dragging using the left and right mouse buttons perform very similarly (though not identically).
LDCad's interface is much more reminiscent of actual CAD/CAM system interfaces and can take some work to get used to. The default viewport behavior is very different from LDD. It also does not have &quot;part snapping&quot; turned on by default but instead uses &quot;grid snapping&quot; by default. It does have &quot;part snapping&quot; available though, as the documentation notes, the behavior can be somewhat inconsistent.
Automatic rotation
Bricklink Studio includes a certain amount of automatic rotation when adding new parts to a model that can help in many instances. For example, if you add an axle to a model, rotate that axle slightly, then add a gear to that model Studio will most likely automatically rotate the gear to fit the axle for you. That said with even a few parts it is likely you will have to rotate one or more parts in order to get them to mesh well in the model. Again, studio does make this relatively simple since you can pretty easily select multiple parts and rotate the collection on a single point.
LDCad does not appear to do any automatic rotation when adding new parts though it does allow rotating multiple selected parts.
Flexible Parts
Bricklink Studio has a very small set of flexible parts and is pretty much limited to axles, hoses, chains, and studded strings.
LDCad includes a much larger selection of flexible parts, importantly for Technic based builds: rubber bands. There is a learning curve associated with using them, but that they are present at all is a huge plus.
Instruction Generation
Bricklink Studio includes a mode that enables relatively easy generation of instructions. I have personally found it to be pretty decent but still need to usually tweak the output a bit to make some steps clear.
I did not find any default support for instruction generation in LDCad but since it is using LDRAW files by default it would be relatively easy to use those files in one of the several instruction generators that are available separately.