This is a tier list of all Genshin Impact characters (a.k.a. units) that can be obtained from banners, based on their perceived effectiveness, ease of use, and value in typical endgame content. 5-stars are assumed to be C0, while 4-stars are assumed to be C6.
Tier list
Dominant tier
These are the best units in the game. Most optimal teams will include at least one of them.
Bennett (off-field Pyro): a staple buffer and healer for most ATK-based carries.
Chevreuse (quickswap Pyro): the cornerstone support for Overload teams, Chevreuse also deals respectable quickswap damage when built for it.
Furina (off-field Hydro): An unconditional hydro applier who provides a teamwide DMG% buff, she is a top contender for nearly any team that deals talent damage and has a healer to counteract her HP-drain.
Kazuha (off-field Anemo): The best Anemo unit overall, he provides grouping and DMG% buffing, and he can perform certain double-swirl VV setups. His infused burst provides additional off-field elemental application.
Mualani (on-field Hydro): a Vape dps with the highest damage cieling in the game.
Nahida (Dendro): the best Dendro applier and EM-buffer.
Neuvillette (on-field Hydro): does almost as much damage as Mualani while being more consistent and comfortable to play.
Sucrose (Anemo): comparable to Kazuha. Which is better will depend on the team.
Xilonen (off-field Geo): Like Kazuha, Xilonen shreds enemy resistances and buffs the team's DMG%. She has no grouping but provides healing to the on-field unit.
Excellent tier
These units are versatile and competitive in the current meta.
Alhaitham (on-field Dendro): works very well on Quickbloom teams.
Arlecchino (on-field Pyro): high-damage but high-risk dps.
Clorinde (on-field Electro): self-healing dps with short uptime.
Cyno (on-field Electro): excellent Quickbloom carry with Furina, Ororon, and Baizhu.
Emilie (Dendro): With her signature weapon and C6 Bennett, Emilie can deal excellent on-field damage. She also does great off field in a team with Pyro application.
Faruzan (off-field Anemo): C6 Faruzan is a crucial teammate for Xiao and Wanderer.
Fischl (off-field Electro): The best all-purpose Electro dps, Fischl is a staple for Aggravate teams.
Gaming (on-field Pyro): plunge-attack Vape/Melt dps with a high damage cieling that makes him the best 4-star on-field carry if you can handle his playstyle.
Kuki (off-field Electro): Her ability to trigger Hyperbloom from off-field while healing the on-field unit makes her important for many Hyperbloom and Quickbloom teams.
Lyney (on-field Pyro): a high-damage but high-effort archer.
Navia (on-field/quickswap Geo): best Geo dps, can frontload damage with her skill.
Ororon (off-field Electro): excellent in teams with Electro and Hydro or Natlan units.
Raiden (Electro): Still one of the best on-fielders due to all the utility in her kit, Raiden is also one of the best off-field Hyperbloom triggers.
Wanderer and Xiao (on-field Anemos): excellent with C6 Faruzan.
Wriothesly (on-field Cryo): best Cryo dps, does well with Bennett+Xiangling+Furina.
Xiangling (off-field Pyro): still the only off-field Pyro dps for now, and quite strong.
Xianyun (off-field Anemo): required for most plunge teams, great healer for Furina.
Xingqiu (off-field Hydro): best off-field hydro applier, assuming you can drive his burst with normal attacks. He does less damage than Yelan but provides defensive utility.
Yelan (off-field Hydro): provides normal-attack-driven hydro application and damage along with a DMG% buff for the on-field unit. She pairs well with Furina or Xingqiu.
Good tier
These units can be strong in certain teams or situations, but are not quite "top tier".
Baizhu (Dendro): very good Dendro healer who also provides periodic shielding.
Beidou (off-field Electro): good against pairs of enemies, provides defensive utility.
Charlotte (off-field Cryo): good healer to pair with Furina to make Freeze teams.
Chasca (on-field Anemo): single-target Anemo dps who doesn't need Faruzan.
Childe (on-field Hydro): His team with Xiangling, Bennett, and Kazuha is famously versatile in the hands of a skilled player.
Diluc (on-field Pyro): best used with Xianyun+Furina as a plunge-Vape dps.
Hutao (on-field Pyro): single-target dps with a high damage and skill cieling.
Kaeya (off-field Cryo): good for Melt teams, especially Arlecchino Melt. Note that his c6 is unusually hard to get and his Cryo application suffers without it.
Kinich (on-field Dendro): single-target dps who synergizes with Emilie and Burning.
Kirara (off-field Dendro): very good shielder for Aggravate and Nilou Bloom teams.
Klee (on-field Pyro): good dps with a playstyle some find clunky.
Kujou Sara (off-field Electro): specialized buffer for Clorinde or Raiden.
Nilou, Kokomi, Collei (Nilou Bloom units): Nilou's teams with Hydro and Dendro units are very good in most AoE situations. Her best teammates are Nahida, Kokomi, and Collei.
Noelle (on-field Geo): performs very well with Furina in a Hydro/Geo team.
Rosaria (off-field Cryo): good for Melt teams. Unlike Kaeya, Rosaria only needs her C2.
Thoma (off-field Pyro): good shielder for Burgeon, Mualani, or Chevreuse teams.
Yae Miko (Electro): A favorite Electro off-fielder for Spread teams, Yae Miko can also do well on field in Aggravate or Quickbloom.
Zhongli (off-field Geo): Though his shield is strong, Zhongli usually represents a trade of potential team damage for comfort. He is a great counter to enemy Geo shields.
Alternative tier
These 4-star and standard-banner units are decent alternatives to premium units.
Barbara (Hydro): a free substitute for Kokomi, and a decent teammate for Mualani.
Candace (off-field Hydro): works in Nilou Bloom, Arlecchino Vape, and Mualani Vape.
Sayu (on-field Anemo): decent 4th unit for the Bennett+Xiangling+Furina core.
Dehya (off-field Pyro): decent Pyro applier and defensive unit for Kinich or Clorinde.
Dori (on-field Electro): At C6, she is a decent Hyperbloom trigger and healer, particularly in a Quickbloom team with Furina, Nahida, and Fischl.
Heizou (on-field Anemo): decent Anemo dps for Aggravate or Faruzan teams.
Kachina (off-field Geo): provides DMG% buffing via the Hero of Cinder City artifact set.
Keqing, Lisa, Sethos (on-field Electros): acceptable drivers for Aggravate or Electro-charged teams.
Jean (off-field Anemo): accessible healer to pair with Furina and use the VV set.
Layla (off-field Cryo): has the second strongest shield in the game.
Lynette (off-field Anemo): can provide VV shredding and a taunt for a variety of teams. She's also a good sub-dps for Faruzan teams.
Mona (off-field Hydro): provides a strong but brief DMG buff, good for Vape teams.
Ningguang (on-field Geo): does well with Furina, Bennett, and Xilonen.
Tighnari (quickswap Dendro): popular ranged Spread dps for single-target situations.
Xinyan (off-field Pyro): decent shielder and Pyro applier for Mualani Vape.
Yanfei (on-field Pyro): does reasonable AoE damage for a 4-star, and can generate a shield sometimes at C4.
Yao Yao (Dendro): an alternative to Baizhu as a healer for Aggravate.
Yunjin (off-field Geo): A decent buffer and Crystallize "shielder" for Wanderer or Clorinde.
Obsolete tier
These units either compare unfavorably to similar ones or have kits that don't function well in typical endgame content.
Albedo, Chiori, Gorou, Itto (mono-Geo units): mainly used in off-meta triple- or full-Geo teams which cannot use C0 Xilonen as a support.
Amber (Pyro): Most useful in the early game and when solving puzzles, Amber is crucial for new players but doesn't perform well in typical endgame content.
Ayaka (on-field Cryo): inconsistent due to her reliance on Freeze to keep enemies in her burst and activate her preferred artifact set, Blizzard Strayer.
Ayato (Hydro): obsolete in comparison to Kokomi and Neuvillette.
Chongyun (off-field Cryo): provides a Cryo infusion and cooldown reduction at C2+. Unfortunately, these benefits are not currently relevant.
Diona (off-field Cryo): Her main use-case is in a Gaming Melt team which relies on many stationary abilities ("circle impact") and thus is not consistent.
Eula, Freminet, Mika (Cryo/physical units): could be relevant in situations where physical damage is desired. So far, no such situation has arisen.
Ganyu (on-field Cryo): outdated Cryo dps – Wriothesly is preferable.
Kaveh (on-field Dendro): appears to be a 4-star alternative to Nilou, but doesn't do a good job of it.
Qiqi (on-field Cryo): The worst 5-star unit in the game, Qiqi has no energy generation, and her teamwide healing is tied to her weak on-field attacks.
Razor (on-field Electro): His meme team with Nahida, c6 Bennett, and a hydro unit can be decent against groups of enemies immune to knockback, but there are better ways to use Nahida and Bennett.
Shenhe (off-field Cryo): mainly used in Ayaka teams – see Ayaka.
Sigewinne (off-field Hydro): There are other healers who do more for a team.
Venti (off-field Anemo): His style of grouping isn't applicable to most Abyss content nowadays. Kazuha is much better.
Yoimiya (on-field Pyro): There are a lot of better Pyro on-fielders to choose from.