Apparently you can steal a Ragnorak from one of the final forms of Kefka, but I don't know which one. Yes, The sword is better to get. While the esper Ragnorak teaches you Ultima, you can learn Ultima from the Paladin shield. So this method takes a while longer as you have to uncurse the cursed shield, though it is worth it.

Another question, does anyone know of any good items that you can get through morph if you take the esper?