It's always going to be Lex for me. But businessman Lex.
He's my favourite Superman villain, he's my favourite villain of all time in general.
He has such an extraordinary kind of power, gained by this great facade of being the philanthropist. He's the absolute definition of a psychopath to me, but at the highest level of influence... which is just so terrifying.
I like the idea of a villain that cannot be beaten - not because he is too physically strong, but because he has too much sway. Over the public, over the government, over important people in power. He's smart and he's patient and he always covers his back.
He basically represents everything that is wrong with the system. Greed, corruption, people turning a blind eye and taking bribes, being intimidated into silence. A second hand criminal with no accountability.
Everything that Superman is basically fighting to change, is personified in this man. And so in a way, Lex represents the first hurdle in fixing the system... it just happens to be a very very hard hurdle to complete. He's the best. He's the first domino in a way... take him out and all the other corrupt parts of the system start to loose their nerve, start to make mistakes in their haste to not fall the same way.
People underestimate the strength of that kind of villain within a story.