Eden
Non - Elemental
Eden is the only GF capable of damaging by more than 9999 and can be quite easily boosted by 250. As well as being powerful in battle Eden also has useful abilities like devour to raise your stats and the very important GF Abl Med-RF. With Eden you can customize your GF's abilities.
In the Deep Sea Research Centre after defeating Bahamut go further down the area until you reach Ultima Weapon. Eden can be drawn from him. However the hard part is actually beating Ultima Weapon. Eden can also be found in Ultimecia's castle.