Poll
19%
15%
4%
11%
52%
Morgoth hands down. We're talking about Evil for Manwe's sake! Morgoth was not corrupted or a servant of the Shadow, but he IS the Shadow itself. He's the Evil personified, (or Valarified 😛 ). He was the source of all Dark and Evil in Arda (actually technically it's Eru since Morgoth came from him but I'll just shut up now). At least Sauron and Saruman wasn't really Evil at the beginning, they were just corrupted by power and might.
When it comes to Evil, nothing surpasses the First Dark Lord. 😈 😄
Morgoth is still the greatest. Whether if we're talking about power or evilness.
Sauron in the Second and the Third Age tried to dominate Middle-earth, and he almost did in the Second Age, if not for Isildur. But Morgoth? He didn't. He didn't just try..he did. You remember "Arda Marred"? This was due to Morgoth's control over Arda. He had complete control over all the world. That is, until the War of Wrath when he was finally defeated and cast into the Void.