Out of the mains, Achamian, he's the anchor of the series to me. He's so disillusioned with the world and his life at the beginning then comes to find love and faith, only to have it torn away from him, along with what remains of his sanity. Not to mention the circumstances. He realizes Esmenet truly loves him only because of the reality that the Second Apocalypse is beginning (and she believes him. And he finds belief in the man who has seduced and impregnated his wife. Akka's story is the embodiment of the epic absurdity that defines the series.
My favorite character to read though might be Eleazarus. His arrogance and obsession with jnan made him so fun to read, not to mention the contradiction that he's supposed to be someone who knows what's going on behind the scenes yet he's so clearly been played.