Who should I give Atk Tactic to?

I just recently got a new +Spd/-Res Siegbert which is better than my previous +Res one. I want to fodder the old one off for Atk Tactic 3 for my mixed teams but I have about 3 mixed teams rn and none of them use fliers. I don't have a 5* Titania either.

I have Ike and Shiro for Def Tactic; L'Arachel, Spring Sharena and Summer Leo for Res Tactic and L!Lyn with Erika for Spd Tactic.