I don't want to give too much away, but Nihilism fits very well with Darth Nihilus' theme.
Darth Sidious was obvioulsy insidious, what manipualting politics for 20 odd years to become evil dictator of the galaxy.
Vader = Father is pretty obvious.
Darth Maul is a bit of a stretch, I admit, but he is the most viscious fighter--taking on two Jedi at once and holding his own. Douku lost to a single Jedi who wasn't even in a fit of rage as ObiWan was when he killed Maul.