Modern mechanical engineering CAD for 3d stuff is pretty good if all you want it something that a 3d printer could spit out, indeed it mostly seems to be going the opposite way of photo and video editing. Understand one's workflow (they vary a bit, though mostly it is the difference between 2d sketch to make things and 3d bases to others and how much you use constraints) and it becomes like image editing once you understand and actively make use of selections, layers and layer masks.
Have a look at something like
http://www.ptc.com/product/creo/elements/direct-modeling/express or
http://www.123dapp.com/ (it is from autodesk, I preferred their old free program of inventor fusion but this is not bad either and is fairly well supported among the home 3d printer set).
You start needing crazy parametric stuff, needing to use nurbs like a big boy or full analysis/testing and you probably want to pay, or possibly try to use some of the open source stuff (doable, not pleasant though) or even kick it old school and go full 2d (there is some very good free stuff there).