Like Miltiades, I was also satisfied with TSL's ending (the long talk with Kreia worked just fine IMO).
The worst ending that that I've seen was of a little known game called Darkstar One. After the obligatory "saving the universe by killing the evil aliens", you're still flying your old rustbucket and the "girl of your dreams" runs off with another guy.
But from the choices above - Dragon Age 2.