If you were to pick one focus school for use specifically with the Operator, which school would you pick?

This is for starchart play and, at most, Sortie 1. Pretend you have all waybounds available, so you are only looking at the upgrades for your three abilities (Void Dash/Blast/Mode) and any applicable passives.

Personally, I would pick Madurai. I don't know if the elemental passive affects your Amp, but the Void Mode upgrade that increases your damage for every second spent in Void Mode would be helpful for trying to take someone down with burst damage (with the T1 scaffold, it's almost a 12% boost in damage just for pressing your crouch key before charging up the attack). Also, not important, but the fireball Void Blast just sounds cool. I can't find a good use for Madurai's dash abilities, though.

Unairu is a close second for me, with its Void Dash upgrades (50% less armor and damage to any enemy you hit), but it isn't useful against lightly armored enemies or bosses. And since you can use Void Mode to negate all damage (and take very little damage when you shoot to leave Void Mode), the damage reduction will hardly be noticed if you hide in Void Mode and shoot at your enemies while under cloak 90% of the time. It does, however, get points for being semi-useful in group play, since Void Mode allows you to make your allies invisible, but only as long as they stay somewhat close to you. (Maybe it would've been useful in that Kuva Fortress Defense Sortie, if you could maintain Void Mode for a decent amount of time.)