Favorite to least:
Ifrit, Cerberus, Alastor, Nevan, Gilgamesh, Beowulf, Rebellion, Yamato, Sparda, Lucifer, Pandora, Force-edge/Yamato combo, Agni and Rudra.
I don't know what Nero's arm is considered, I would say a devil arm (no pun intended) because its a weapon and humans did not create...