Board Thread:General Discussion/@comment-5621713-20121207092202/@comment-2A02:587:C410:3B00:BC52:1CEB:9B1A:F064-20171114120925

Ultimatelly, Merlin is the most powerfull Sorcerer. His magic being a secret, him using it morally, and trying to fullfil Arthur's destiny all are the reasons why we don't see him abuse it the same way Morgana does, and this is why Morgana usually does more impressive things. That said, if we had an amoral Merlin, he has proved able to A) take away the power of Morgana through planting an idol of some sort under her bed, B) Fully Control the 2 remaining Dragons, and his controll has proven to expand to wyverns, whose number is unspecified, but could be numerous C) Use lightning to kill a whole armie in a matter of seconds (though this is after the incident in the Crystal Cave). Using his shee (don't remember how it's spelled, the blue pixie creature thingy) staff, he could use a disintegrating beam, and has proven able to replicate it to some degreee without the staff in his battle with Nimue.

A major theme in the series is Merlin trying to hide his magic, use it undercover, or not rely on it because it would be amoral to do so. Morgana on the other hand does not have such restrictions. In the end, I believe that, wile they are close in raw power (as in what you can measure by a stunning spell) Merlin is superior (as proved in their duel in season 4, when a weaker from the snake, aged Merlin faced a Full Power Morgana and still won). In matter of what they have in their Magical Knowlage, Spellcasting Knowlage and More complex Spells, both have shown a lot of amazing feats. I'll leave it to each to decide, but my vote is again with Merlin, as he has shown ability with many aspects of magic at an astonishing level, and at least some aptitude to others.