RAMUH... should not even be on that list. He's not really all that impressive. It would be cooler if he were a playable character who always had the most powerful lightning spells. But he's some old dude with one spell who is usually quickly replaced by superior specimens. Ifrit is a djinn but looks like a demon, Shiva is genderbend of a Hindu god, Bahamut is a freakin' dragon.

Other candidates: Diablos really is a demon, Leviathan is an Asian dragon, Odin (Squee should do some kind of lore explanation for why Odin uses the Zantetsuken instead of his Gungnir), Kujata is the giant elemental bullpig, Alexander (I've really understood why Alexander is some kind of giant mechanized castle), Phoenix, Ark is a transformer, Eden is the size of a school, Madeen (I personally prefer the IX version), Quezacotl is based on Quetzalcoatl (winged serpentine Mesoamerican deity), Anima is some kind of representation of the psyche (in-game, I don't know what she's supposed to be), The Magus Sisters.