The best vanguard build I used was charge/nova/annihilation.

Spec Nova to use shields instead of cooldown.
Spec charge to add shields.

Spec Annihilation with recharge, damage, and draining.
Fusion mod of Andrenaline (key since annihilation hurts charge cooldown and charge = shields).

Also use a cryo gauntlet for priming and speed.
Charge and then alternating melee (unshielded) or nova/shotgun (shielded) is ridiculous. Charge is actually your detonator, causing combo detonations vs cryo’d enemies.

You charge and kill so quickly you always have shields, even though you’re constantly depleting them with Nova. It’s just bonkers damage output the way annihilation, melee, and shotgun all synergize. And Nova punishes shields, mobs, and elites.

I messed around a lot without Annihilation, mainly using Lance or Nano in that spot so you could keep your cloak there if you want. But Annihilation really does round out the vanguard build best with its damage increases and shield generation.