And um, merely for posterity's sake, I ramble here.
Thar be spoilers.
In the great battle of eeeeeeevil, why do I go kind of guh when it comes to evil!Sam and go OMG *hides* when it comes to demon!Dean?
Baby, you know I'm gonna bring up the Farscape don't you? Scorpius. Fucking scariest bad guy ever. Patient, brilliant, and radiated anger and power under his skin. Waiting for the right moment to strike and when he got angry, WHOA. He will fuck up your shit. Or EAT YOUR BRAIN. SERIOUSLY.
...or make you bite off and EAT your own finger just to make sure the mind control was working. That is some fucking evil.
Really, the demon!Dean in Dean's head is more a Harvey-figure in Dean's head than a Scorpius type. That doesn't mean that he's less dangerous. Prior to John Crichton neutering Harvey, Harvey did take over John's body and caused some pretty dreadful actions that had consequences for the Farscape crew.
I may have been discussing with Stef about writing a story where Dean still has demon!Dean in his head, taunting him and whatnot. Perhaps my Farscape is showing too much, but MAN. Demon!Dean is fucking crazy and will not stop. Evil!Sam is scary too, oh yes, and I enjoy the scary, but there's something far more powerful in an unhinged monster that knows how to maximize the pain. The Megified demonified Sam we saw in Born Under a Bad Sign was more mocking and didn't seem to have that Scorpius-level of fucked up evildoing. Who knows, maybe a really eeeeeevil Sam would hack that and be scary.
But man. There's something about demon!Dean.
I'll be sitting on my hands not writing that, right now, okay?