Fire Emblem: Three Houses! Order here is kinda random, starting with lords/good duellers and then working through characters largely by weapon type.
Edelgard has great offence, quads the below average for ORKO damage and doubles average with Silver... but what really sets her above the pack is Raging Storm which basically forces you to decide how much you let legendary weapons be spammed. I lean towards only allowing one use of this per fight, but even with that she still kills average as soon as she gets a turn. Not having uber evade or raw durability means she's far from perfect, but still Heavy/Godllike.
Dimitri is just a big ol' pile of stats. Quads average for just shy of ORKO, has great evade (just at full HP, but that's enough), yon standard Really Good Fire Emblem dueller. Probably belongs in Heavy but he's really scary there if so.
Claude has similar offence to Dimitri, though doesn't have the same Def and relying on Alert Stance for bonus evade isn't as good as Dimitri's personal. On the other hand he has two nasty tricks Dimitri doesn't: Encloser to ruin melee opponents, and Fallen Star to grant him one turn of perfect evade. Also a really scary Heavy.
By comparison
Byleth doesn't stand out nearly as much. There's a Nosferatu gimmick build but it's just so undamaging, and the offence is 3RKO unless s/he fights someone slow enough to be doubled by Brave. Still, regen on someone with no problem stats could be worse. Good Middle.
Besides the lords, the best tier of duellers includes
Ferdinand,
Petra,
Felix, and
Catherine. Standard FE goodness. All easily double average and have good damage, and evade on top of that. Petra is probably best due to having high damage and Alert Stance. Catherine needs Thunderbrand to reach that offence but isn't too far behind using Brave, while Felix has lower durability and base damage but is even faster and has a regen option for what that's worth. Ferdinand has extra evade at full HP. Heavy one and all.
Ingrid has terrible damage but doubles everything with it, so not so bad in practice! And she has loads of evade and good MDef. Her lance-using buddy
Sylvain has a game-plan of 2RKOing your face with Swift Strikes while having only averagish speed but solid def.
Seteth has less damage than Sylvain but plays a similar game, but Alert Stance is neat, as is Spear of Assal regen as an option. All three go to Middle, though Ingrid at least seems like a scary one.
Hilda will have you know it's hard to argue with an axe to the face, low 2RKO with Brave Axe with some options to double the slow, and Apocalyptic Flame does only slightly lower damage but the str debuff may let her take an extra hit from physicals, and she's already quite physically tanky. Good Middle.
Cyril is faster so he can double average with Silver, but just misses a 2RKO even so due to lower strength; the slow fear him though, and he has Alert Stance. Good Middle which is more than he deserves.
Ashe is a worse Hilda in every way: damage, durability, AS, you name it. Probably still swings Low Middle.
The War Masters offer good damage but bad speed.
Dedue is the best of them, tieing Edelgard for game-best damage (and at low HP Vengeance pushes him even further) but doing so gets him doubled by average, unfortunately the above average will double him regardless, so Middle. His excellent pdur softens that nicely but magic makes him explode.
Raphael is a bit slower so average always doubles him, he's still durable but not as much, Light/Middle.
Caspar and
Alois both have a bit less damage and considerably less defence but a fair bit more speed, unfortunately their only 2RKO damage still gets them doubled by average, Low Middle.
The archers...
Bernadetta just has bad durability and damage both, but she's saved somewhat by Encloser, which once again ruins melee fighters. Vengeance is a cute trick as well I guess. Light/Middle area.
Leonie barely quads average with a Brave Bow, which is a low 2RKO, and if she misses that double she has Point-Blank Volley, and unlike Bernie her durability is fine. Middle probably.
Shamir is trash, she can Hunter's Volley for low 3HKO off her game-worst durability, Light. And
Ignatz has gone swordmaster instead of Archer; he's got Ingrid's damage but his quads are far from ironclad (and if he misses that, the offence is terrible) and the evade is far more fair, but he brings his archery to bear with his 144% silence combat art, so is Middle.
Everything doubles
Gilbert. The pdur still wins way too many fights in Light though, so probably Low Middle for the character oft considered the worst in the game. Dies to most Light mages.
Mages are in a rough position generally. The star is Magical Swordgirl
Lysithea; dark magic may be DL trash but doubling average with a Levin Sword is certainly legit. Too bad her defence is so bad, but she still makes Middle. Opera stars
Dorothea and
Manuela try to copy her gameplan, but Dorothea has only averagish speed while Manuela has substantially worse damage. Both have regen at least so are very scary Lights at minimum.
Hubert tries to play this game with a magical lance instead, but it gets him doubled by average, oops. Dark magic still sucks, 0.67 pdur sucks, decent Light is all he amounts to.
Linhardt can uh... go 5HKO damage with Fire, or use anything else and get doubled by average, regen and Nosferatu can help but only against mages or those with truly bad damage.
Mercedes is a bit better on damage/speed at least, but has the same core problems.
Annette has considerable more oomph with her legendary magical axe, but otherwise has all of Linhardt's problems, including average doubling her as soon as she uses anything but her weakest tome.
Lorenz is more durable than the other nerds but still has their core problems. Lights all around.
Marianne is different enough to be notable. Her Nosferatu is not only a bit more damaging, but she also doesn't get doubled by average with it. The fast double her... flipside she can use it to double the slow, with Darting Blow. Add that on to her regen and she's a pest to kill unless her opponent is speedy. She can also double average with her legendary weapon but the damage isn't anything special. Probably still a Light, but she's actually a good one, maybe a borderliner even.
Flayn is the comedy option. Between Nosferatu, Renewal, and Caduceus, she can regenerate ~70% of her HP every turn! She's also doubled by average and has game-worst pdur, so anyone with 4HKO physicals beats her anyway. Mages explode at least? Too bad they're rare in her division, bad Light. Might be the worst dueller, but that honour probably goes to...
Hanneman is what you get when you take the Linhardt stat build, and give him -9 AS from average with his lightest spell. Oh and he doesn't get Nosferatu or Renewal. He DOES get 100% silence off of... a 22HKO damage combat art. Hope you allow him two Silver Bows! (I do.) But that's still only useful against people who can do literally nothing while silenced. Light/Puny borderline.