It is kinda subjective. But I think that Eshonai was basically just honor, and caring for her people, thrust in a role she didnt want. A good character, but we have similar ones already.
Venli is hungry for power, sided with Odium, realizes that she is doing the wrong thing, and has to try to become like Eshonai, while fighting the feeling that she can’t and isnt worthy.
I think that Venli is more unique to SA. And to me personally, she is defenitely more appealing.