Best users of Steady Stance 4?

Xander and my main man Julius

Slow, high-def units or potentially even someone like Jagen because with +8 def he actually gains quite some bulk.

Can also be good on Fae, especially if you don't push her spd really high

On armors it pairs well with slow vengeful fighter users who don't need a breath skill (Zephiel, H!Myrrh ect)

Xander might be the unit that gets a boost from it the most. With it he might be one of the most allround physical walls, since special blasters won't do anything to him.
And being a cavalier makes it fairly easy for him to avoid magical matchups.

It should go to cavalry or flying units who otherwise lack any excellent A skills as they can't learn any Breath skills. Units like Xander and Beruka, who only really fear specials from defense targeting foes, would be top choices