Generally the Nin or attack buff for tthe type your using migh be best, Tenten is okay as she will buff the enire team's crit intead of say Mei only effecting water types but most team comps only rely on one ninja to do everything tthe other ones are there for buffs or utlity so i.e Kakuzu EGF skill broken you'll want Onoki for the nin dmg or SoSP/Edo Minato you might want Gaara. Though you'll want to unlock as many as you can since there a decent power boost.