Originally posted by allfg
I'd personally give it to Bandon, and quite comfortably too.
http://www.starwars.com/databank/character/darthbandon/
Powerful emotions like anger and hate raged within him, and they fueled his strength.
His great strength in the Force, his natural cruelty and his absolute ruthlessness in his quest for power soon set him apart from his fellow students, and drew the calculating eye of Lord Malak himself.
Darth Bandon proved himself to be an excellent choice. Many Jedi fell beneath the blade of his lightsaber.
Some in the Sith hierarchy wondered if Bandon would someday rise to challenge Malak for the mantle of Dark Lord
In other words, he was picked out of an entire order of sith by Darth Malak to be his apprentice (which included people like Traya, Nihilus and Sion), he had faced and defeated many jedi in combat, many believed he had the potential to surpass Darth Malak, and he embodied all of the ideals of the sith.
Statwise, he's not even that far less powerful than Malak (that is when he appeared on the Leviathan, not the Star Forge).
There's also the fact that he was able to effortlessly slam a sith trooper into a wall with some pretty tremendous force.