Sasori Analysis
Main Win Conditions
Sasori's only win conditions seems to be poison and Iorn Sand from looking at his profile and I'll go into detail below.
The Iron Sand is Sosari's only chance at survival. It holds over a 4x AP advantage (as shown in the OP and thus can block almost any physical assault from Tomura with the exception of "Decay". And though the Iron Sand is incapable of killing Tomura through standard smashing on top of him or stabbing (Unless he crushes/stabs his skull) him due to his high level of regeneration (Mid level), it can be used to attack at a microscopic level and poison him. And yes, while the poison takes 3 days to kill, it's incapacitation time happens right after it enters the target and leaves them crippled.
I see no resistance to poison either on Tomura's page either so that seems to be Sasori's best bet. His other abilities are not used in a consistent manner or would be effective in my opinion but I'll just mention them below so no one could claim inaccuracies.
Supportive Abilities
While he has it, Sasori doesn't use the basic ninja stuff such as Minor Illusion and Duplication, Shapeshiting, or Paralysis Inducement. But I don't believe those (with the acception of Paralysis) would be effective since Tomura has "Search" which allows him to monitor up to 100 people at once so he'll never lose track of Sasori even if he makes a clone or transforms.
Performance of a Hundread Puppets is almost a non issue. Sure, it gives Sasori a small army and since they are all in the air, Tomura's "Decay" won't tag them but that's about it. They are too weak to harm Tomura and thus can't properly deliver their poison, and "Search" would allow him to keep track of the all. Finally, a single Air Cannon that has Tens of Kilometres of range will wipe them out due to them baing to weak.
Sasori's regeneration will no be much of a factor since Tomura is so strong, he'd shatter the puppets beyond just their limbs being dismembered and if he sees Sasori using their limbs as back ups, he can just decay the remains on the floor. Finally, Body Puppetry is helpful but the main issue Is Sasori doesn't have the lifting strength needed to out muscle Shigaraki who is Class T so he can't proporly manipulate him.
Tomura Shigaraki Analysis
Main Win Conditions
Tomura is able to one shot Sasori and any of his puppets due to the gap in AP. Decay may not be able to hit Sasori's puppets (Because all of them minus the Hiriko puppet float in the air) but it can tag Sasori which will force him to jump to avoid it whenever he's on the ground. Decay can also be used on contact so he could decay any puppets he physically comes into contact with, though he's strong enough to one shot them.
He massively out ranges Sasori with Decay and Air Cannons so unless Sasori blocks with Iron Sand (Against the Air Cannon) or jump (Against Decay) he's screwed. Speaking of Decay, it can be used to get rid of the Iron Sand "if" Sasori attacks with it in large solid forms which he occasional does but if he decay's ome block, Sasori won't be stupid enough to send another and will recognize the danger (though if Shigaraki uses Decay right from the start, he'll no not to send the Iron Sand in chunks).
Supportive Abilities
Search will allow Tomura to keep track of Sasori and his puppets so surprise attacks are likely going to be ineffective, plus will allow him to know Sasori's weakness is his heart though most of his attacks will decimate Sasori as a whole. Tomura's Mid level regeneration will allow him to survive but Sasori mainly goes for poison so I don't see thos being too big of a factor but it's notable.
His range/aoe with Air Cannon will allow him to blow away any poison gas and Impact Recoil should be capable of at least stopping some of the impact of large block Iron Sand. Wing and Air Walk will allow Tomura to keep pace with Sasori's puppets if he attempts to send them high up. Warping wil allow him to escape the area if need be but I don't think it will be necessary. (Note: It was cleared up in a comment below that Tomura can't warp himself)
My Vote
I vote Tomura.
He's got the AP, Range/AoE, and Abilities to one shot Sasori and his puppets. His supportive abilities can help him deal with or avoid the Iron Sand and poison without to much trouble. Meanwhile, Sasori's best win condition is using the microscopic Iron Sand to inflict poison on Tomura and incapacitate him. However this won't be easy because of the pressure Tomura would apply in battle with his large scale attacks that would constantly keep him on the move.
I just see Tomura having more of an edge than Sasori, so I'll vote for him.
