The advantage of Hercules is that she is extremly tanky with her self buffs that last 5 turns. That is basically one less character you need to worry about, which can ease up the overall overview of fights. Besides that she is a good investment for longterm usage. Water has some single target healer, so keeping that in mind, I would take Herc (besides another possible def debuff, as mentioned from her Relic, having literally free choice what to use as Ex-Skill).