g1smd - 7:28 am on Aug 3, 2013 (gmt 0)
I would always go for a page-by-page redirect.
Assuming you use Apache, point the DNS for both hostnames at the same hosting space and add:
RewriteRule (.*) http://www.example.org/$1 [R=301,L]
to the root htaccess file after all other external redirects and before any internal rewrites.
Make sure that you also convert all Redirect and RedirectMatch rules to instead use RewriteRule syntax.