Which of the two does more damage? I mean, making blizzbrand, blazebrand, and silent night blade feel like a waste, when looking at how this can do a lot more damage.
Avenger vs Blizzbrand on Slag Walkers.
But the thing is, with the Blizzbrand (or the Glacius, it's upgraded version) can cause freeze, which could be helpful at keeping the Slag Walkers at bay. Just freeze the suckers and then go after Vanaduke!
It's much better to bring a shivermist if you wanted a freeze effect. A shivermist+DA pairing makes the glacius quite obsolete in the FSC.
Its up to your preference really, both swords are great. I prefer my blizzbrand over my DA because I hate slow swords and the DA(The Avenger as well) slows you down when you are charging it. And with DA or Avenger if you are too close to walls when firing the charge attack the "swords" will explode as if they're hitting the wall.
Remember the Avenger is a 2 swing sword but does more damage per hit with strong knockback, though the second swing is very slow and if you miss you'll be open to attack. Avenger series charge attack is more powerful but you slow down when charging it.
Blizzbrand does 3 quick swings that overall do more damage but wont knock back the enemy out of range of you at times. but you'll maintain speed when charging which will allow you to do hit and run charge attacks which is my play style.
Personally I prefer the Glacius or even Combuster over Divine Avenger for FSC. I do damage just about as quickly because of the improved speed but I take much less damage as it's easier to defend. For Vana himself, switch to DA since he's not weak to Elemental as the zombies are.
_brand has better DPS (damage per second) 1v1.
Divine Avenger deals more DPS and has knockback to safely fight hordes of monsters.