I've used I-DEAS, Pro/E, and Mechanical Desktop. The best I've used is I-DEAS, since it is the most straightforward and flexible (of course for some people these are mutually exclusive). Mechanical Desktop is just a pain in the neck, and Pro/E is somewhere in between.
Ford and Nissan use I-DEAS as does Toyota (I think).
Harley-Davidson uses Pro/E (I think it's the only vehicle manufacturer that uses Pro/E).
Caterpillar used to use Pro/E until the lawsuit - I don't know what they use now.
Among high-tech companies: Raytheon uses both Pro/E and some I-DEAS (and speaking from experience, even where they send out the final product as having been designed in Pro/E - the major part of the actual designing (as opposed to modeling) was done in I-DEAS). Boeing uses Unigraphics and I-DEAS. Lockheed-Martin uses I-DEAS, Catia, Unigraphics, and an internal software. Hewlett-Packard uses their own software. TRW uses I-DEAS and Pro/E. Kodak uses anything you like to use (since there are translators available for just about everything).
My advice would be to learn Pro/E, I-DEAS, and Catia - you will have many options ahead of you. (The only problem with learning I-DEAS, however, is that you will see many more flaws in all the other CAD software that might frustrate you).