My argument is for AKA II Quadfather (MUT23). AJ Dillon.
He was so broken they had to nerf him in less than 1 week.
Freight Train that did not turn off, persistent (which required 2 TFL to deactivate) and Bruiser. I think at release that was all for 2 AP. That card was ridiculous to play against. I couldn't afford him until after he was nerfed.