The most powerful good characters

[The Squatter of Amon Rûdh]

But that's only if we don't count the Valar, then you would have to give the award to Melkor. Eru says this himself (I think, could be wrong)

You're not wrong about Ilúvatar's statement, which is

Mighty are the Ainur, and mightiest among them is Melkor

(Ainulindalë)

However, Lúthien is still the greatest of the Eldar, regardless of whether or not you count the Valar, since they are Ainur, not Elves. Of course if you really meant that the Valar constitute the most powerful of the beings living in Middle-earth, I should say that this thread is about the most powerful good characters, amongst whom I never count Morgoth Bauglir.

That discussion was hilarious, Rimbaud. Thanks ever so much for the link. I hope that we'll be seeing a lot more of burrahobbit's illustrative charts in future.