I think there should have been a few more choices, especially if the question is who is the most evil:
I present some more options:
Pinhead from Hellraiser
Thulsa Doom from Conan the Barbarian
The Darkness from Legend
The White Witch from Chronicles of Narnia
Ming the Merciless from Flash Gordon
Ra from Stargate
Xerxes from 300
Alessa from Silent Hill
Skynet from The Terminator series
Uuuhhhhh...no. Xerxes? Anyone from Silent Hill? Stargate? Seriously?
My choices, which I'll explain again, were based on the following criteria:
1) A major, relevant, epic, sci-fi/fantasy, film series
2) An evil MASTER (note not
apprentice)- Sorry Vader fans but he's Palpy's B***H!
3) A Dark Lord who is all powerful, obsessed with conquering death, and whose presence is felt throughout multiple heroes' arcs
4) They had to at least appear in a film as an active villain (hence why Morgorth or any of the other Sith MASTERS didn't make it)
5) Grand schemers
6) Pure evil. Non-sympathetic villains.
These four have a lot similarities IMHO.
(Yes we know little about Thanos at this point but we can still glean a lot from the film and the literature. The latter of which you all seem perfectly willing to do for Sauron and Voldemort, FYI.)
They all have:
1) Armies at their disposal
2) An "Enforcer"- Darth Vader, Bellatrix Lestrange, Loki, Witch King of Angmar
3) A Mouthpiece- Mas Amedda, Peter Pettigrew, The Other, Mouth of Sauron
4) An obsession with "conquering" death- Thanos in quite a different fashion, lol.
So that's why I picked these four. I'll call them the "Big Four Dark Lords"; since IMHO they represent the four largest franchises going.
Keep it going gang. Sauron's running away with it at the moment.