AudioBridge, I don't think there IS a difinitive suggestion, and wars have begun by saying that there is.
MY answer would be in two parts:
Google SketchUp is freakishly intuitive and it's free. But it's not very versatile. (Not as versatile as many other packages at any rate.) To get your feet wet, this might be a place to start.
Blender (YAY! Blender!) is NOT intuitive (until you learn it, then it becomes like breathing), but it IS versatile, it's ALSO free, and it has a community that is almost rabid in it's willingness to help.
Pretty much any 3D app has an almost straight-up learning curve, so be ready for that. Get one that strikes your fancy (another reason to go for the free stuff to begin with) and expect to be building simple things for a little while. Just hang in there. Crawl, walk, run, fly, warp drive, right? Eventually you will be Dennis Bailey or Vektor!