Playing on Maddening/Classic on chapter 13 now:
Best: Lapis by far, I used her since chapter 7 and used some boost items on her (the free bonus ones went to Alear). Promoted her to Swordmaster on Tiki's Paralogue while I was in chapter 9 and used mainly her (with Marth), Alcryst and Alear (promoted) to kill all the reinforcements waves, at the end of the Paralogue she was lvl 6 and had turned into a crit/dodge machine. Chapter 10 she alone trivialized one side of the stairs dodging and doing crits on everyone.
Disappointing: Alfred. I benched him after giving Sigurd's ring to Louis and since then Amber has filled his shoes when I needed a lance cav. Being a royal I was expecting more from him but he was useful only until chapter 5.
Worst: The twins, Clanne was benched really fast by Celine (and she was benched by Citrinne) and Framme was used as a heal bot until I promoted Citrinne and then benched.
Not as good as Lapis but helping a lot are Alcryst, Diamant, Citrinne (Brodia is carrying me hard), Louis and Alear (all promoted). Chloe isn't a powerhouse but being a Flier is useful on some maps but now with Ivy joining she is in danger of being benched. Jade and Amber are ok but situational, Yunaka was great with Micaiah but now with Zelkov i don't know what will happen to her, Kagetsu was good on chapter 11 but with Lapis/Diamant/Alear I don't need another sword infantry. Etie/Boucheron/Jean/Anna/Vander are all benched until the end of the game. Fogado, Bunet and Pandreo are too new to say anything and Ivy being a mage flier already gives her a place on my team.