<this is just my opinion, but to me, thats what counts>
Solidworks is by far the most user friendly and powerful software out there. The capabilities are tremendous, it runs well even on my older PC's, and it is also easy to learn and intuitive.
Autocad is very good for 2D, but 2D is a thing of the past. The real world is 3D. I understand that layouts will always be 2D, but any decent 3D software will have a capable 2D platform built in, you just have to learn to work with it. It has it's place, and will continue to rule the 2D world for the foreseeable future.
ProE (now CREO) is probably very powerful, but is extremely difficult and annoying to use. I've had no trouble learning Solidworks, Autocad, Inventor, NX/Unigraphics and a host of other proprietary programs, and I am able to do things in ProE, but I just hate it. Too many questions and confirmations before you can actually complete a task, and the buttons/menus don't lay out logically for me.
Since I work for Siemens Energy, we use NX/Unigraphics because we own them. It is not as easy as Solidworks, but is probably more powerful, and is VERY good for CAD to CAM because all of our CNC programming is done in NX. It also interfaces very well with Teamcenter for file/project management, since that's another Siemens PLM product.
Manucad is still the fastest program, and is what I used to help the concrete guy understand how to layout my slab for my shop, among other daily uses.