I never played Daggerfall (couldn't get it to run
), but as far as originality and lore goes I vote for Morrowind; Oblivions idea of using portals to some dimension seemed just a bit clichéd, as well did those goblins.
Nevertheless the graphics and fighting are better and I'm still having a ball with all the mods available for Oblivion. The Natural weather mod is amazing, and Shivering Isles too ofcourse.