Could go either way. It wholly depends on the time period and the Circe which we're talking about.
armandovalles
who's Circe? u mean Sersi?
Draco69
No. Wonder Woman's archnemesis. Directly based of the Circe of myth. Ya know. Turn men into animals? There was a JLU episode on it.
DigiMark007
I'd vote Loki, but since the amalgam tourney I'm biased. He's always written as a coward that loses to Thor, but if he was ever written at even half his max potential he'd be a preeminent villian of Marvel. Ultimate Loki (unless Ul. Thor's crazy) is winning at the moment, so hopefully he's more of a badass.
Of course, I know nothing of Circe except from mythology books, so this is basically just a rant.