Which L!Hector IV’s?

I'd say it probably depends on what special you want to run on him, with +Def Ignis/Bonfire are going to do more damage. The +Atk one works better with his default special though.

L!Hector's Atk is high enough that even -Atk doesn't hurt him too much though, so I'd probably just focus on having higher Def/Res to make him take less damage from other armoured units.

Sorry if this wasn't of much help to you.