Darth Bane: Formed the OTS and recruited the first generation. Oversaw the recruitment of the first member of the Second Generation, but left soon after his arrival. In my personal opinion, a great recruiter, but a horrible leader. The majority of the First Gen look up to him, but I honestly never liked the man's role as Dark Lord.
Darth Ruin: A great motivator, who kept people in line and rallied up during his short reign, but essentially a do-nothing Dark Lord. Though, if I remember correctly, he did oversee the demolition of a Jedi uprising at least once in this short time period; which in all consideration is a huge accomplishment.
Darth Malice: The least effective, and overall inactive, Dark Lord. I was the man's 2nd in Command, which says a lot about him. I mean, I'm the lovable slacker. You can't put the lovable slacker as #2. So, basically, I handed all the duties that were put on me during his absence on Al's shoulders. Which is why I sometimes refer to Malice's reign as "The Shadow Reign of Dark Lord Draknor".
Darth Draknor: The most effective of the Dark Lords, in my opinion. He took a hands-on approach to the training of apprentices, and helped and/or completely trained all of the 4th, 5th, and 6th Gen. Sith, as well as some of the 3rd Gen. A surge in recruitment took place during his reign, as was noted by the number of generations he either trained wholly or helped train.
Darth Vol'jinn: I haven't been in the Sith during his reign, so I honestly don't know. I didn't even know he was Dark Lord until today. :/