Many people won't know Vitiate so this kind of isn't fair but imo he's the more evil one. Sidious is pretty bad too though.

Vititate wanted to consume all life in the galaxy so he is by far way more evil

^Sidious pales in comparson to that

@Polygoon And Sidious wouldn't?

Vitiate murdered 5000 of his own kind as a young man to make himself immortal.

Depends on how we're measuring their evil.

I have to go with Darth Sidious