Talent priority

Some characters need their whole kit to function optimally. Others only use parts of their kit, with some talents not even being used at all. And then there are some characters that care most about their passive talents (leveling their active talents not even necessary).

This can happen when the character provides a special ability like crowd control or buff via passive. The introduction of dendro and hyperbloom has made it so that many hyperbloom comps only need three elements to react to do damage (and could care less about talent level). This makes certain teams easy to build, if you do not have to care about talent level as much.

Note most characters will use E and Q when played in teams (with few exceptions). Not every character will use their normal attack. Or even if they do use their normal attack, it may be just to drive reactions (such as Nahida NA for hyperbloom).

Talent level up priority
Talents Characters
All 3 (use whole kit) Xiao, Itto, Diluc, Eula, Alhaitham, Scaramouche, Yoimiya, Lyney, Qing, hu tao, Ayaka, Aloy, Wrio, Klee, Freminet, Yanfei, Noelle, Razor, Heizou, Faruzan, Yelan (if care about CA dmg), Kazuha (if care about plunge/E/Q dmg or C6)
E+Q (many sub-dps, healers) Dehya, Nahida, Cyno, Raiden, Venti (if care about damage), Yae Miko, Childe, Ayato, Focalors, Yun Jin, Beidou, Candace, Rosaria, Kaeya, Fischl, XQ, many healers (Jean, Qiqi, Yaoyao, Barbara, Mika, baizhu, Charlotte), Nilou (if care about non-reaction damage), Sucrose (if care about damage), Kokomi (if play as burst dps: as kokomi is hp scaling, the atk scaling in her NA is less important the hp scaling gained from the Q buff), Amber, Collei, Thoma, Xinyan, Kirara, Lynette, Lisa, AMC, DMC, EMC, GMC, HMC
AA+E
AA+Q Ganyu, Tigh
Q Mona, Bennett, Chongyun, Kaveh (Q buffs reaction), Xiangling
E Albedo, Shenhe, Kuki (for healing), Gorou, Sara, Morax, Layla, Kokomi (if just care about E off-field healing)
AA Noctis (whole kit including E/Q droplets is designed for CA)
None (characters that do their job even with lv1 talents) Venti (if just care about cc), Sucrose (if just care about cc/battery), Kazuha (if just care about passive/cc), Nilou, Raiden (if full EM hyperbloom)

Crowns

Crowns are a somewhat limited resource in Genshin, with many obtained via limited time events. Table highlights which talents are worth crowning. We focus more on 5 star units. It is generally not recommended to crown 4 stars unless they are truly exceptional (e.g. Bennett Q).

Which abilities to crown
Talents Characters
All 3 Xiao, Itto, Diluc, Eula, Alhaitham, Scaramouche
AA+E Yoimiya
E+Q Dehya, Nahida, Cyno, Yelan, Yae Miko, Childe, Focalors
AA+Q Lyney, Ayaka, Wrio, hu tao
Q Mona, Raiden, Bennett, Venti, Yun Jin, Faruzan
E Albedo, Shenhe, Gorou (to maximize def buff), Navia
AA Noctis (fully operational even with lv1 E, Q), Ganyu (esp. for melt)
No crowns needed Most 4 stars, Qiqi, Jean, baizhu, most healers, Morax

Beyond lv10

Some things in the game can increase talent levels beyond lv10. This includes constellations, Childe's passive, some event effects. Different characters benefit from boosting different talent levels beyond lv10. Some benefit from boosting all, while some only need to boost one or two.

If a character can only pick one or two talents to boost beyond lv10, then there are talents that have certain priorities to optimize overall dps.

Also prior to 4.0, all characters' constellations would give +3 levels to E or Q. 4.0 is the first version to introduce characters that can get +3 levels to NA. If we could rewind time and change the constellations of pre-4.0 characters, which talents would we choose to give +3 levels to?

Boosting 2 talents beyond lv10
Talents Characters
E+Q Xiao (c6), Dehya, Nahida, baizhu, Cyno, Yae Miko, Morax, Childe, Yelan, Albedo, Shenhe, Kazuha, Ayato, Nilou, Jean, Qiqi, Focalors, Aloy, Kokomi, Beidou, Yun Jin, Mika, XQ, Barbara, AMC, GMC, EMC, DMC, HMC, most other characters
AA+Q Xiao (c0-c5), Itto, Eula, hu tao, Scaramouche, Lyney, Wrio, tigh, ganyu, Ayaka, Keqing, Noelle, Kaveh
AA+E Yoimiya, Diluc, Alhaitham, Freminet
Q (does not matter if AA/E) Kaveh
E (does not matter if AA/Q) Gaming, Xiaogan
AA (does not matter if E/Q) Noctis

Most important talent

Most important talent to level
Talents Characters
Q Mona, Raiden, Cyno, Venti, Yelan, Jean, Faruzan, Yun Jin, Bennett, Kaveh, XL, XQ, Charlotte, Barbara, DMC
E Xiao (c6), Alhaitham, Nahida, baizhu Albedo, Diluc, Shenhe, Yae Miko, Childe, Focalors, Xiaogan, Morax, Ayato, Qiqi, Kokomi, Kuki, Kirara, Thoma, Fischl, Mika, Gorou, Yaoyao, HMC, most E subdps / E healers / E shielders
AA (usually main dps) Xiao (c0-c5), Eula, Ayaka, hu tao, Scaramouche, Itto, Wrio, Yoimiya, Lyney, Noctis, Keqing, Ganyu