Darth Bane and Darth Zannah vs Darth Malgus and Hero of Tython
DoE Bane and Zannah take on False Emperor Malgus and SoR Hero of Tython. Standard gear and abilities, all are fighting all out (perfect chemistry for both teams), and the fight is to the death. Battle takes place on Arcann's flagship and they start 15 yards apart.
Who wins and why?
Team 1. Since most didn't answer the why: Bane and Zannah have actually fought as a team, lending them even better synergy than a newly formed alliance. Bane speed blitzes, Zannah defends herself when necessary, and when an opening presents itself she goes all Force Sorcery action on Malgus and the Hero. That alone is enough to do Malgus in by itself, and even if the Hero could recover, he/she could not do so before being cut down by Zannah or Bane, or fried into nothing by Bane's lightning.
Zannah at that point could possibly even destroy Malgus' mind at range without even needing to get close, as Malgus has no showings indicating that he could resist it. Regardless, team 2 dies every time.