[fjtorres]

Assuming that copyright length can be changed--which is doubtful--I'd favor life + 25 or 50 years, whichever comes later. That will provide for orphans and widows and posthumous works.
Corporate works? Unchanged. With trademark and all the legal tricks out there the nominal length of their copyrights are just that: nominal. In practice, the corporate types will always have a fully copyrighted work that protects their interests in a given franchise.
Dragging them in will only make any effort at change impossible instead of nearly impossible.