Kreia. To me, she's the female version of Palpatine from ESB and ROTJ. Scheming, manipulating, etc.
Malak is just the stupid schoolboy bully who stole the big stick from the guy who was supposed to use it, and now goes on a whacking spree to show how bad he is. Stupid evil as apposed to clever evil.
Whats with all the Darths anyway ?!?
I'm pretty sure that in most parts of the games, they are referred to as Malak, Revan, Sion, Kreia etc. There might have slipped a Darth in there, but I suspect it's something all the Darth wannabes are attributing to them. Heck, I can't even remember Nihilus being called by his name, he's usually just "Visas master"