I've had some amazing results with all of them, except Baharroth.
Asurmen has killed a reasonable amount of things and has survived 6 game turns of CC with a Soul Grinder (A feat in itself).
Karandras infiltrated and killed a squad of Plague Marines turn one. Handful of similar instances.
Jain Zar ate many Terminators and Marines in her day.
Fuegan did his thing all over the place, even down a DP in CC once.
Maugan Ra has been my fall back guy for some time, being almost as good a Jain Zar in CC.
However, since I can't let Baharroth lead over anyone, I am going to vote for Jain Zar. She's done well enough to deserve it.