Who should be? Shiro-4. He's experienced and certainly has the rep to command authority. Ana is too......self centered to be a good Vanguard. I mean she ditched the City in the middle of Twilight Gap. Who will most likely become the Hunter Vanguard? Crow. In my opinion he's too inexperienced to be a good Vanguard. But in all likelihood he'll the next Vanguard because no other Hunter wants it, Crow however just wants to be accepted. His past as Uldren also means most Guardians, especially Hunters, won't be too accepting at first. And the Reef-born Awoken may or may not like this decision. Uldren did lead a whole war on his own people.