who to give steady breath to?

hi! so i've been wanting to ask this for a while but i didn't get a chance to until now. when i was trying to pull for h!kagero on the new halloween banner for fodder i ended up getting another brave ike and i already have one with +atk -hp iv's. the other one is +res -hp and i'm thinking about giving steady breath to roy or black knight. who makes better use of that skill?