Who do you think is the most interesting bad guy shown in the SW-EU? Not the most successful, or powerful, both of those would probably have to go to Darth Sidious.
A good bad guy should have multi facets, he's not just evil for evils sake, or for power. Despite the horrible prequels at least it showed an good journey to the dark side.
For that reason I really like Revan. I think they show a really dynamic story line for him. I might be biased as I am playing KOTOR now but I think he just makes a great bad guy.
Vader is an obvious choice with a good story. But also an obvious choice.






