+Atk -Def or +Atk -Res for Brave Ike?

I'd suggest getting rid of the +Atk - Def Ike.

I’d keep the +Atk/-Res one since his Defence is more important and works better with his kit. But if you want to run DC or have him duel dragons and tank mages better then +Atk/-Def is acceptable since his Defence is high enough as it is. Although +Atk/-Spd is better in that case.