As far as the absolute strongest I feel like that can be measured in impact on the Narrative, and impact on Paradox Space. To that end, I think Alt Calliope is the most powerful bc she's successfully been the Narrator for several parts of the story, and she turned herself into a black hole to consume the Green Sun, which is probably the single most impactful thing we've seen happen to the cosmology of Paradox. A close second would be Lord English, who killed the Horrorterrors and cracked all the black space, and as Caliborn controlled part of the narrative. Then Dirk, who is in control of the narrative, but he hasn't made any big moves yet re: paradox space.

Below that I feel some of the other most powerful characters are obvs like Vriska for being Helltier, John with his retcon powers, Jade for having the power of the Green Sun, etc. Although, I think Vriska is easily the most powerful of them at the present moment cause like. John has no retcon powers. And Jade's link to the Green Sun has been severed.

Some characters that I think people aren't considering who should be in conversation are Davepeta and MSPAR. Davepeta is the character we've seen do the most damage to Lord English, and in fact as far as most characters are concerned or know, Davepeta is the one who killed LE. (who know it's really altcallie but I think only Aradia and Davebot also know about that). MSPAR has both the retcon powers and at the end of Pesterquest, the powers of the Green Sun. Granted, they now reside in a "Locked" timeline, whatever that means, but that itself is a significant act of control over the Narrative/Paradox Space, so honestly maybe MSPAR should be up there with LE, Al, and Dirk? Davepeta I feel is at least on the level of Helltier Vriska, Retcon powers John, and Green Sun Jade.