>>712705503aran is technically the best target if you just want to have a reliable way to clear db chapters, he has the best growths and abuses the bonus exp mechanics the best
jill being a wyvern does not matter much because the dawn brigade chapters are all defend chokepoint chapters where you want to stat deathball and hold points
if you want a unit you just want to use for the dawn brigade arcs aran
if you want units you want to use for the tower zihark or edawrd
jill just stands akwardly in the middle
forgot to mention that she needs forged axes just to hit enemies because hit rates in the early game are really shaky meanwhile the other characters i mentioned do not have hit issues because they cap skill at lvl 10