"If you truly wish to relinquish ALL rights then public domain is exactly that. This is obviously the most free. If additionally you wish to retain attribution only then /usr/src/share/misc/license.template is a great choice. This is probably the most free except for public domain. If it bothers you if Microsoft uses your performance in a Vista ad then you must pick something else.
"There once was a message to test; Repeated unto being a pest; While marked to ignore; It was seen more and more; Until other begged, 'Give it a rest!'"