Autodesk Inventor is great, but has a somewhat steep learning curve (to master all its options, especially simulation), but perfectly suited for this sort of modeling and design, this was some fun I was doing with Inventor getting to learn it.
http://www.rc-monster.com/forum/showthread.php?t=31671
Now Autodesk Autocad, also is non dispensible as a CAD program, but mainly its for drafting, although can handle 3d, not as nice as Inventor. I still use it for fast drafts or checks, or if i need to import any drawing for CNC'ing. I find it faster to just start drafting something and take some measurements and check an idea.
The problem with these programs, I feel you will tend to get a biased answer, or a brand loyalty, for instance I have used Autodesk: Autocad, 3dsmax, and inventor, and hence have not tried other brands to give you more feedback.
Nontheless shoot your questions, maybe we could help in answering some questions you have.