User blog comment:General MGD 109/Who's most powerful?/@comment-80.167.120.171-20150426181645

As I see it, Sigan demonstrated magic never seen before (before Merlin I mean). His power is great without a doubt, but Merlin was still abel to seal his soul back into the crystal which put Merlin in a greater spot.

Morgana sure has great power and she uses it freely without thinking of consequence. The reason she can always surprise Merlin is due to her status as a high priestess - she knows more about dark magic than Merlin, not meaning that Merlin could not do the same but greater. And in S2, Ep. 11, Kilgarrah says that Morgana does not have the power to wield the crystal - Merlin can wield the crystal with little to no effort.

After Morgana tried to take Merlins power by the use of that creature, Merlin got his powers back with the guidence of his father saying that he wields powers he cannot yet understand - truely understanding his true power once he got out from the cave of crystals.

One more evidence that Merlin is more powerful than Morgana could ever dream of becomning: In S5, Ep. 4 Morgana uses the ageing spell to conceal herself as princess Mithians waitress: as a consequence the only thing she can do under the influence of the spell as to stun other people. But later in the same season (I am not sure what episode) Merlin under the influence of the ageing spell uses a spell more powerful than anything he has ever used before: the spell that frees Gwen from Morganas will.

All in all Merlin is, in my opinion, the most powerful wizard to ever work the earth with powers far surpassing Morganas, but I do not know the full extend of Sigans powers compared to either Morgana or Merlin.