Strongest in terms of the team being well rounded. A strong hitter, magic user, someone who can get crits, someone who can tank both physical and magic damage, healers, long ranged unit.
I'm sorry if this is such a vague question haha. I am just paranoid about having the strongest everything that I want my team to be pretty good. Also, I heard that you can buy skills from others? How do you go about doing that? I think that this would save some time grinding for some good skills.