I think a more appropriate question to ask is "What do you want to design with your new 3D package?"
While all these packages are good, they each handle different things better than others.
My experience is with Pro/E, SolidWorks, Inventor/MDT, and Think3. Personally, I didn't have anything that Pro/E couldn't handle (if you have the money), and SW is still better than Inventor, for what I do now...
Write back and we can help,
Mr. Pickles