Archimago - Being able to pull out another powerful spell a second time can really turn games around. Just a powerful effect to have at our disposal.
Battlemage - Against early aggression getting to draw a card and remove a minion for 1-3 life seems pretty decent in a pinch. Combine with something that negates damage like Goswhit Helmet or Royal Bodyguard and you've got a good time.
Interrogator - If we find ourselves able to strike the enemy avatar a couple times this can easily put us at enough cards to keep up the pressure or switch to a different avatar. Or they can eat 4+ damage a couple of times, either way.
Ironclad - If we believe to get chipped for 1-2 early we can rush into defense stance. Not the best against some midrange decks but can prevent a lot of damage against aggro. Again, combined with the damage negators makes for a very strong defense.
Necromancer - I feel as if getting tokens on board early open up a lot of possibilities for this deck. Could be one of the go too avatars to choose as soon as we can. I'll have to really play this one out to know.
Realm-Eater - Really only here if we find ourselves needing to remove a problematic site or to prevent them reaching a key threshold. Very niche, but it's a decent option.
Savior - Once we start to deploy our main threats we might wanna make sure they are a little resilient while on the approach. Or if we need to make our early threats stick we can rush into this mask and give lots of protection that way.
Sorcerer - Draw a spell. Need I say more?
Witch - A little bit of whatever we might need. Extra damage on each turn, slow down for a tempo shift or even counter the niche Battlemage/Bladedancer. Good against midrange decks.