So, I had a random thought about who became Vanguard first between Zavala, Ikora, and Cayde-6. I realized while digging into it that, while we know who was in each position before, the events around that time are a little confusing.

First, the basics:

Previous Vanguard members Andal Brask Osiris Saint-14

Our Vanguard Cayde-6 Ikora Rey Commander Zavala

Next, we know what led to each of the previous members leaving the Vanguard

Andal Brask killed by Taniks Osiris exiled after Twilight Gap Saint leaves to find Osiris.

Ok....so from what I've gathered this is the order of events through the full transition of Vanguards. (Please correct me if I have this wrong.)

1)Osiris leaves before Twilight Gap 2)Saint-14 leaves to search for Osiris 3)Zavala is named Titan Vanguard 4)This one has three parts that all happen at once, during the same meeting of the Vanguard and others, A)Ikora is named Warlock Vanguard B)Osiris is officially exiled C)Zavala is named Commander of the Vanguard 5)Andal Brask killed by Taniks 6)Cayde-6 (see what I did there, hehe) is named Hunter Vanguard.

It can be inferred that for a time, Warlocks were without a Vanguard after Osiris left the Last City, yet Zavala was promoted to Titan Vanguard likely immediately after Saint-14 disappeared. At the time of her being named Warlock Vanguard, Ikora had been Acting Warlock Vanguard, performing the duties for some time before being given the official title.

All of this leads me to believe Zavala was first to become Vanguard of OUR version, but it's possible that after Osiris left Ikora was doing his job BEFORE Saint-14 went to find Osiris. This would mean Ikora Rey would, in fact, have the most Vanguard experience. I could be missing something entirely, so please correct me if I am.

In case anyone else was curious, there ya go haha!

EDIT: Osiris leaves before TG