FE1!Marth - Murdermachine. Once he got Mercuruis he became unstoppable (except by Camus, but he's a different scenario)
Alm - Murdermachine, if a bit low movement-wise. Once Silk got Warp, there was always a plan B - throw Alm at it. THEN he got bows.
Celica - OK, but not great. She was always glassy, but dealt insane damage. Leveling her to 20 in time for promotion was a pain...
FE3B1!Marth - Meh. Loss of infinite rapiers definitely hit him. Then there were other chas who got better (Like Barst)
FE3B2!Marth - Started strong, but eventually slowed down a bit. I get the feeling he will demolish final chapter, though.
Sigurd - Never gained speed which bit him in the ass later on. Still hit like a ton of bricks and was tougher than Ardan so that worked unless enemy had Pursuit.
Seliph - Carried a Substitute Run on his back. Well, he, Leif and Ares.
FE5!Leif - Was okay until about chapter 14, then hit a level cap. Got better after promoting, getting Leg Rind and a few levels.
Runan - Slow but powerful. Had a penchant for overkilling people with Rising Dragon.
Holmes - Bows are overpowered in TRS, and so was Holems. Do the math. Never needed swords on him until the final boss.
Roy - Murdermachine until he hit the levl cap. Still wiped the floor with Zephiel after promoting and then critblicked both Jahn and Idun. Infinite Boots helped a lot.
Lyn - Typical Lyn. Nothing much to add.
Eliwood - Tank to the end, ended up maxing his def both before and after promoting. His Str and Speed were unremarkable.
Hector - It was weird to see a speedy Hector with less defense then Eliwood.
Eirika - She was alright, A-support with Seth made her crit about half the guys she fough by midgame.
Ephraim - He was awesome, until he hit his stat caps. In the end he ended up worse than Eirika in anything but defense.
FE9!Ike - 14 Str by Endgame. Not cool, Ike. Ne couldn't even scratch both BK and Ashard and got doubled by them, forcing me to escape/rely on Ena and Giffca. Aether didn't help much either. What a letdown.
Micaiah - Well... she exists. Devs screwed her up big time.
FE10!Ike - Now there's the Murdermachine!Ike we all know and love. He still got demolished by Nolan in 3-13.
FE11!Marth - Just bad. He was worse than Leif and bare ended up not getting doubled by Medeus.
FE12!Marth - Back to his FE3 self.