The strongest state of Sukuna in after the battle promise and before the battle with Gojo Satoru.

His kit is immense. Ten Shadow, Shrine, Complate Transform and Kamutoke.

After the fight with Gojo, he obtain WCS but heavily restricted. Its probably strongest attack in JJK(invisible and cutting anything) but after binding vows attack become predictable and avoidable. Plus Sukuna with maximum output can kill anyone(expect Gojo Satoru ofc.) with dismantle.

The being reincarnated sorcerer disadvantage is losing body control to soul attacks(Theres just few attack can do that Yuji punches and Shrine, Nobara's CT, Yuta and Hana Jaccobs Ladder). But you cant land that strikes(only can Nobara) on Non weakened Sukuna, so they arent threats really.

Factors

Ten Shadow: This CT so versatile in hands of jujutsu god.  He can use shadows and shikigami abilities. 

Top of that Ten Shadow contain two of the three strongest non-sorcerer being(Mahoraga, Agito, Rika). 

Mahoraga is the triumph card. He have 15F Sukuna capabilities(after a few adaptation). 

Sukuna's shadow Mahoraga is maybe not strongest(this part controversial, some people say its stronger Megumi Mahoraga or Modulo Mahoraga(like Sukuna's Nue), some people say opposite but my point isnt that) but most dangerous. 

I said that because Sukuna so smart and talented. Almost impossible to exorcise Mahoraga.

Sukuna can summon Mahoraga's Wheel and semi manifesting him and just uses his ability. 

If Sukuna didnt manifest Mahoraga completely you cant destroy him and he adapts and adapts.

Another hand theres Agito. I think its really underrated. This Shikigami can tank Gojo's BF and heal instantly. And it can fight with Gojo.

Probably stronger than most heavy hitter and its easily special grade sorcerer strenght.

It can heal Sukuna constantly.

We didnt see all its capabilities, i assume its equal to Rika or little stronger.

Kamutoke: Special Grade Cursed Tool. I think if Sukuna uses Heian Era and today this should be stronger than his Shrine. Because theres no point for Sukuna using assault tool weaker than his CT.

It can be effective aganist sorcerer. In jjk nervous system is important. Kamutoke can strike that system directly.

Its uses lightning attacks and lightnings speed are 1/3 of  lightspeed. Its almost unavoidable attack.

Shrine: Sukuna's innate CT. He can create invisible slashes. Very useful attack focused CT. Critic part is so hard to sense it. 

Sukuna have very strong combat ability close-mid-distant combat.

Malevolent Shrine: Sukuna's open domain expansion. It dont posses a barrier, Sukuna use that for enlarge the sure-hit effect area(to maximum 200 meter radius).

MS untankable in standart conditions. Single cleave attack can kill a sorcerer like Ryu(one of the most durable character in verse). 

In the MS both cleave and dismantle rain relentlessly.

Divine Flame: Ability of Shrine. It have some conditions, using after MS creates little nuke.

Sukuna True Form is hell of buff.

This part controversial but i think this form giving Sukuna huge basic stats increase(we cant confirm because he take that form after battle with Gojo and his output was decreased and his brain fried.)

Several times mentioned, body determines reinforcement effectiveness.

So my take is in this form he is massively stronger(term of strenght, speed and durability).

Extra two arms gives enhanced combat ability and advantage.

Most importantly extra two arm and one mouth gives Sukuna huge jujutsu capability(chants and signs).

My opinion is thats the Prime Sukuna. 

The Prime Sukuna