I use raw-text instead of binary because it seems better for
Windows, OS/2 or DOS, namely raw-text canonicalizes line break code.
Maybe "Content-Transfer-Encoding: binary" is not used for mail/news in 
normal case.

Note that emacs-mule of Emacs 20 is not existed in XEmacs/mule.
no-conversion is as same as raw-text in XEmacs 20.3, however it is as
same as binary in Emacs 20.  In addition, XEmacs 20.2 (or older than
it) does not have raw-text, so no-conversion or binary may be better
if backward compatibility is preferred.

  Best regards,
-- 
tomo.