Another Ephraim

Just got my second B.Ephraim. He is +def/-res.
The first one is +hp/-def.
So I already inherited to the first one DC and aether but didn't start leveling up, waiting for double SP weekend.
This is probably a no brainer, but is it better to keep the +def one and merge the other one into him? I liked the idea of him having 26 res (without buffs) to better tank mages and dragons.