IMO get the Vanguard helm. Reasoning: Aside from the "starless night" perk (which, I admit, is awesome), a benefit from the Saint 14 helmet was the abilty to get extra Super energy from PVE kills. Zavala now has a helmet that gives you that same perk. Shaxx has it too, actually. Bought a helmet from him yesterday that gives me extra super energy from grenades AND from PVE kills, so it´s great for my playstile. With that helmet, if you want to go Striker you will still enjoy the extra energy and you will have an exotic slot available for pieces like Ruin Wings or Armamentarium. Should the need arise, switch to Saint 14, but unless the enemy is charging headon at you (like when Thralls do their Zerg rush), other Exotics offer better synergies. IMO the glasshouse may be a better helmet for anything that isn´t melee related (more time for Weapons of Light? Where do I sign?). I´m still going to keep my Saint 14 helmet, but probably won´t use it outside of some Nightfalls and the Crota raid now.

The upgrade isn't available yet

If u plan on doing Vault of Glass, Helm of Saint 14 has good perks for the Defender subclass, which is essential on the Raid.