Well, like you said, Ramza is a pretty killer hero of the story. But Delita isnt a villain, you see his whole theme in the game is "Do the Ends Justify The Means?" I mean, he manipulated practically everyone in Ivalice, killed some people, and all of his efforts were just for his lusted power. But on the good side, he did lead Ivalice into a land of prosperity and ended the reign of the nobles.
My favorite villain is by far, Wiegraf.
To me, Wiegraf was the perfect villain. In most villains, one can find some type of common ground, something to humanize them, or conversely they are shown to be evil to the core. While both types make good villains, Wiegraf actually begins the series with a noble cause and a strong belief system. He acts as a foil to Ramza, in that they both had lofty, noble aspirations, and they both fought for the sake of their sisters. Ramza easily could have taken Wiegraf's place in the story, at least as far as giving in to the desire of the stones to prolong their lives. But when Wiegraf lets go of everything he once believed, it makes the player actually hate him. To me, his actions actually elicited a degree of emotional response, which is unique to most videogame villains that I've ever come across.