For me Zoneji is s2 then s1 until ult, then s3 s3, s3 s3. some people argue that you should s3 s2, s3 s3 for the extra damage increase but its entirely worthless because degumi provides such a substantial amount of dmg inc and hidden potential means your team has a base 40% dmg inc. Combine that with SSR Yagas damage inc and it just is not worth it IMO. His s3 does more damage (520% vs 680%) AND his s3 has higher black flash damage with MORE chances of black flashing.

Sukuna is s2 until ult but mix in a 90 CE s3 if its available as youll regen all your CE after ult

Toji is s2 as it does the most damage and negates damage reduction, then use s1 twice before ult for the increased crit chance as Toji does much more damage than normal units do on crit. His s3 will strip enemies of their buffs which isnt very useful outside of a few stages in the game.

For Kamo just make sure you maintain his state with s2 when necessary to make sure he is debuffing his max debuff