I don't really like Legends, sorry if this list seems messed up.
10. Darth Plagueis
9. Darth Malgus
8. Darth Vitiate
7. Darth Caedus
6. Exar Kun
5. Darth Bane
4. Darth Maul
3. Darth Sidious
2. Darth Revan
1. Darth Vader
Ah ah ah ah ah ah ah ah aaaahhh blllllllll ah ah