Enlil
Ok NOW I'm gonna go to sleep.
Mostly I'm good for either as both are in combat threads (but not duesl) right now. If you want to test your characters just straight up power and skills, go with Salis. She's far more experienced than Shavara and has the power to back it up.
If your more reliant on the force then on weapons, and want to test their creativity mostly, then Shavara. Her robes make her extremely difficult to damage or manipulate through the force, and her sword has some unique traits to it.
Between the two, Salis is better in almost every way for combat aside from that her weaponry and alchemic abilities are inferior. Shavara is a good person and a lightsider however, while Salis is quite the opposite.