For me it's Zemo, all the way.
That guy started out as just another very smart, still cheesy supervillain with a horrible fashion sense. Just that he wasn't 'super', he was just smart. Not as smart as Tony Stark or Dr. Doom, though. So rather meh.
And then I read him on Thunderbolts: He was a good fighter, smart, devious
but in a good way, a villain that made giant plots to
help humanity for a change, and still he managed to be so absolutely snotty, that I wondered whether to laugh, or to get angry.
Example: The Thunderbolts are on Counter Earth, and there are some dudes who want to destroy Paris. Zemo: "But why do you want to kill them?...They
are French, though..."
But he really got me when he gathered the power of all the heros and villains on Earth, just to cancel his and the Grandmaster's powers and finally kill him with a simple Luger (that dude was an elder of the universe, yo!)
Made me read up on all the old Thunderbolt comics, you should try them too

And I just can recommend you reading the last mini Zemo: Born better. Close to never have seen such a good characterization, while there still is action.