autodesk is a company name, they have multiple programs, they now have maya, 3ds max, autocad, motionbuilder, and i think even revit
i personally use maya 7, i hear bleh things about maya8 (the first version release since autodesk has bought out alias) so i'm sticking wtih maya 7 for now.
but what are you using your program for?
personal work? client/freelance work? or are you starting up a company?
if you are learning software, there are demo's and "personal learning edition" versions of any of the big programs out there.
there are also free programs such as blender, wings3d, etc... just check out the thread in these forums about the free programs...
anyways, let us knwo what you are wanting to do, and we'll help you out. the more the info the better