I talked to my bro since he beat the game.
He says that Delacroix gets his vote because he seems to have the edge over Seph:
he can summon minions, has the Apocrypha of Yzarc, shoots beams (omgzorz!), and his whole plan is more destructive than Sephiroth's Meteor idea.
From Wikipedia:
The protagonist, Sieg Wahrheit, is a Knight of the Dark Glyphs who is on a quest to find his former friend Victor Delacroix, who has stolen the forbidden book Apocrypha Of Yzarc, and to stop him from releasing the spirit Azrail who will destroy the three planes of existence (the Nether World, the Middle World, and the Celestial World).