I'll judge every individual fight here. 🙂
Ventress DD (kinda sith) - wins 10/10
Darth Maul TPM - wins 6/10
Darth Maul TCW - wins 4/10
Darth Tyranus ROTS - wins 4/10
Darth Malgus - wins 0/10, Malgus can Force crush him, or completely stomp him in a duel
Darth Marr - wins 0/10, Bane can't contend, Marr's weakest abilities are beyond Bane's ability to process
Darth Jadus - wins 0/10, Bane is the better combatant and lightsaber only Bane would honestly stomp, but Jadus is so powerful in the Force he can murder Bane by flicking his finger.
Darth Nox - wins 0/10, Nox is comparable combatant and Jadus level in the Force.
Emperor's Wrath 2 - wins 10/10, Wrath is completely outmatched.
Darth Krayt Reborn - wins 0/10, Krayt is just better in everything.
Darth Caedus - wins 0/10, same as Krayt.
Darth Tenebrous - wins 10/10. Tenebrous was a lightsaber enthusiast, and trained Darth Venamis to have perfect knowledge on Plagueis's technique, perfect answers to kill that one singular opponent, and Venamis was full physical equal with Plagueis. Plagueis on the other hand despised lightsaber dueling. Despite that, Plagueis defeated Venamis. I can't even begin to imagine how terribly inferior Tenebrous must have been.
Darth Plagueis - wins 0/10 - same as Caedus or Krayt.
Darth Sidious ROTS - wins 0/10, same as Plagueis, Caedus or Krayt, but it's even worse, since Palpatine is superior to these three on every field.
Valkorion - wins 0/10. Valkorion can basically blink his eyes and atomize Bane's body. He can make him die in unbelievable mental pain with Valkorion barely noticing Bane. He can torture and murder Bane with effortless Lightning sparks. He can tear off Bane's head with an effortless hand touch.