My suggestion is get and try to use both packages, you'll figure out almost immediately which kind of modelling you want to do.
Yes... Very good advice. You have to find what YOU want to use...

The big problem I had with Sketchup is the lack of precision. I could drag and drop stuff to different places. I could get the general shapes I wanted. But to put components exactly where I wanted them never worked. That problem is non-existent in Open_SCAD.