i'm in engineering and use autocad all the time for the 2d work, it's easy to pick up and can be totaly icon based for easy use or comand based if you prefer, or a mixture of both.

catia is the most popular data transfer format in the automotive/engineering sector, as its a very stable 3d program.

mechanical desktop (autocad 3d) is ok for the 3d work but not as versatile as some other design packages.

i've used solid works and hypermill for my cad/cam work but i think the best 3d package is vero.

vero can be used as a fully integrated cad/cam package and is the best on i've seen and used in the 12 years ive used 3d design software.

the easiest and cheapest would probably be hypermill, followed by autocad/mechanical desctop, solidworks, catia then vero being the most expensive.

depends if you want to use it as a hobby or as a career, there are loads of training courses about but none of them are cheap mate.