Mine is Zod or Bizarro.
Luthor, Darkseid, Brainiac.
Doomsday. Comes out of nowhere and does what nobody could do before, kill Superman. On his next outing, scares the pee out of Darkseid.
Lex for killing him in all star superman then learns the secrets of the universe and knows whathe did was wrong ooo and parasite he’s cool
Easily Doomsday. He just exudes a sense of violence that is completely unpredictable and challenging for the Man of Steel.
It’s Luthor. Always has been. Always will be. I think he’s the ultimate bad guy because, like Batman, he has no powers.
Mongol is underrated and underutilized.
Darkseid (Duh), Kalibak, Brainiac and Metallo
Darkseid, and doomsday. Pushed superman to limits!
Lex Luthor and Metallo.
Luthor is the best but my personal favorite is Brainiac
Honorable Mention goes to Doomsday & Bizarro as well.