Lategame mech with 3/3 vikings (thanks for the free upgrades David Kim!), 20 units apiece:
In this situation, attack is better. This is fascinating, I wonder what the determining factors are that swing it towards one side being better than the other? (fwiw, attack continues to be better even if I add 20 more mutas so that they're winning the fight)
In terms of just amove vs amove, its probably attack speed and damage. Marines attack fast and have low base damage, so armor is more effective against that than a viking with does a lot of damage and attacks more slowly anyway. Void rays are probably closer to marines than vikings.
In general though, attack is a bigger priority because you aren't supposed to be taking any straight-up fights that have potential to be close. Mutas are meant to be harassing units, so you need to do as much damage as quickly as possible. And most strategies phase mutas out before you get situations like 3/3 vikings or void rays, so armor kind of gets neglected because mutas are no longer relevant.
You know, sometimes I wonder why when one caster says something wrong and the other caster has to know better, they don't correct each other. Listening to Destiny and Catz, I now know why they leave it be.
I wonder if he's just thinking to himself, like, I have no chance in this series, maybe I can save some face if I go bio all 3 games and be like "well I thought I could win on mind games but he didn't beat me playing my best"? What a bitch.