After I had read some comparisons between Jill and Haar in different threads, I deliberated to start an own thread.
Many people say that Haar is the best character in FE10. He's even banned in drafts.
Imo Jill is overshadowed by Haar. Haar is only better in early game because of his excellent base strangth and defense.
Jill is weakly and fragile, when she joins the Liberation Army. Her base strength is very low, so you have to invest in a forged iron axe and maybe an energydrop, if you want to train her. Though the investment will pay off! Her growths are great. She has great speed, luck and decent strength and resistance growth. However her defense growth is her only oneweakness for being a wyvernrider, but bexp. can fix it. And her caps are insane. She can reach 36 defense (only 2 less than Haar) and 35 speed, which means that she can double pretty much everything in the endgame except for a few swordmasters in E-2.
I love using both, but Jill becomes to be more useful in the endgame especially because of her higher speed cap and the fact she's better in dodging.