Hmmmmm.....great thread.
I'll contribute with my top 5 bad guys from DC / Marvel, although I'll stick to film
versions, as this is a film thread. Just IMO, but here you go !
This is in order of awesomeness.
MARVEL
1. Magneto (either McKellen or Fassbender)
2. Loki ( Hiddleston, a very, very close second)
3. Green Goblin (Willem Dafoe)
4. Doctor Octopus (Alfred Molina)
5. Lady Deathstrike (Kelly Hu, in X2)
and the worst.....Julian McMahon as Dr Doom, yuck ! Although honourable mention for worst sideburns goes to Liev Schrieber as Sabretooth. Strangely, I though Hugo Weaving, who's usually amazing as villains, pretty boring as the Red Skull.
As for DC
1. The Joker (Heath Ledger, feel like I almost don't need to say it)
2. Catwoman (Michelle Pfeiffer was the best although Hathaway was good)
3. General Zod ( Stamp or Shannon, although Shannon gets the edge for having a better female Hench-person, Faora, wow !)
4. Sinestro (Mark Strong, probably the only good thing about the GL movie)
5. Two-face ( Aaron Eckhart, in a very underrated performance, if you include the first 2/3 of the film in which they build the character up, so you feel sorry for him when he gets fried and goes crazy).
And the worst........ Nuclear Man in Superman IV Quest for Peace, although a special shout out for awful puns goes to Schwarzenegger in Batman and Robin.