Owain A skill

https://fireemblem.gamepress.gg/hero/owain

I find this question to be one of the better IV questions. There's actually some subtlety to be had here.

The difference between +atk -def or -res is that he's better at surviving multiple hits, which means fury is potentially less good on this IV compared to other +atk IVs. Brazens, on the other hand, tend to be better with -HP than with -def or -res.

There's also a case to be made for the bond, because with -HP it's easier to activate wrath, which is what he wants to do.

The answer will also depend a little on what seals you have available to give him (either depending on which ones you've forged/upgraded or which ones aren't already taken by other characters).