OK, I think this is a very tricky question. I am going to promote Uraeus or Onatel.
The current meta with the heavy use of minions is making me want to go this route (that and I have the emblems to finish to node 20)
Onatel is always a solid choice and even at 3/70 I was able to ride in her back through the ninja tower. Absolutely could not have done it without her.
I can only get her to about node 10 with emblems
I do feel that Onatel is one of the most important heroes in the game…but does Uraeus win the day because of minions?