Better Galeforce Sibling

I think they're both fantastic Galeforce units. I only have Eirika, so a bit biased lol. But I do see Ephraim alot in AR, seems popular and very effective. They each have different areas where they shine, as you mentioned, so I don't think one is better than the other for all cases.

One nice thing about Eirika is that she basically has more skill options available, since Ephraim needs to use Heavy Blade. So she can run QP, to proc Galeforce against ranged units, and still have a free A slot to help with stats. I use Fury in AR, because it let's her get into Wings of Mercy range more easily.

TLDR: Both are great, can't say either is in all cases better. You luckily have both, they seem like they would make a great AR team together!

ooh...this one is really hard. I'm not sure one is better than the other. Eirika has consistency in special charges but not in doubles (it's possible to block her double by being fast enough); Ephraim has consistency in doubles but heavy blade can go wrong. I don't have Eirika, but I do have more than a bit of experience with being unable to get heavy blade activations when I need them, either because the target is too squishy or has too much raw atk. Against teams heavy in ranged units I think Eirika might be better because that kind of team often has really high atk (ex: Ophelia) and if she needs to tank a dancer at the end, she generally does it better than Ephraim because she can probably survive a hit from a Y.Azura or a non-TA L.Azura (or a lot of other stuff) but Ephraim is likely to get doubled and die. Against flier balls and armours I think Ephraim might be more comfortable because he tanks counterattacks to his def more easily and the forced double can crack wary fighter, plus I think he can potentially hit harder?

Sometimes the question will be settled by what colours you need to or can cover using the unit that isn't the legendary cavalier(e).