WoW

I have to say, Fae is definitely the best unit in this banner.
she has workable speed, or you can just work with her mixed defense.
you can keep her weapon and give her distant counter, she can still have up to 6def/res with her weapon.
or you can just give her the normal lightning breath and give her fortress def/res to always have 6def/res instead of the conditional one.
I am not a fan of melee only armor, so DC will always my option.
if you work around her speed, she can have lightning breath, fortress def/res vengeful fighter, and darting stance or her weapon, DC, vengeful fighter, and darting stance.
I am not sure if she has superboon in spd, but with normal boon she will have 38 spd, which is pretty good on avoiding most doubles.
spd might favor more to her weapon, because she can fire iceberg every fight, with lightning breath, the +1 penalty actually gonna hurt her peformance.
you can also throw her spd away, then use stance4, vengeful fighter, and seal to your likings, be it brazen, bond, CD/DD.
throwing her spd will lock her to use lightning breath for DC, but thank to her getting double she can still fire iceberg every battle.
such a powerful chicken.

Eirika is a bit disappointing for me. I'd rather have her atk 23 and her spd is 36. but well, she is pretty potent support unit, exp with the likes of LEphraim/Walmart/LEirika.
they can go anywhere on the map and still receive 6/5/5 on atk/def/res.

now WEphraim. as much as I like Ephraim, he is not that good compared to WEirika and WFae.
but looks like he is still pretty interesting unit.
he is pretty much a physical grima, so I believe trying to make a 1shot build is pretty potent with his statline.
Glimmer, DC, Wary Fighter, and Fierce stance might be good on him. that way he has 67 atk on EP, and always proc glimmer, and he can have 70 atk with atk boon.
that is without buff, so you can pair him with another armor with hone armor, then smite him into enemy forces, and see him kill everyone with over 70 atk + glimmer.
you can even change his glimmer to noontime for abit healing power, or even change wary fighter to mystic boost and keep glimmer, for 6healing after combat.
the downside, of course if he fails to 1 shot, he is as good as dead without wary fighter.
You can also build his PP, which is quite potent too in my eyes.
he can work pretty much like a Lance Alm with armored boots, trading a brave attack for 2 movement.
he can go in, smack stuff 2 times, then get healed to 100% HP again for next turn.
He will be a good galeforce unit vs hard target, but sadly he cant proc galeforce on soft target because of his broken attack stat.

TLDR: Fae > Eirika > Ephraim
Fae is the most simple but powerful.
Eirika is powerful support unit with her base kit.
Ephraim is quite niche, but powerful
Note that this is just my thought on seeing their stats.