So let's see here...Sentry moves well beyond light speed.
He is far stronger than Thor in his current incarnation.
His current strength maximum is unknown, but he dropped Thor (a Herald Class Foe) with less than three solid strikes.
By contrast; Thanos took down Surfer (who is highly comparable to Thor when it comes to jaw strength, IMO) in three punches as I recall.
...that indicates a VERY similar striking power.
With the difference being that one moves at light speed and can land a blitz of Flash-Like hits for each of Thanos' return strikes.
Thanos has a primary form that is HIGHLY durable flesh.
But a scream from BB can bloody his face. He is not invulnerable. Just VERY hard to harm.
If Thanos were to face a creature strong enough to rip his face off, Thanos would fall.
Sentry has a form that is solid based mostly on his subconscious will.
His primary form is energy based. Not solid. He exists as a full controlled body of molecules.
This allowed him to reform from beyond blown apart by Molecule Man.
This allowed him to blow Owen apart in return.
It allowed him to assume the energy/octopus form of Void.
It allowed him to tank hits from a Herald with no evident damage or effect.
It has allowed him to rip his own face off, and show the meat below it to Thor.
Something that Thanos would risk self-K.O. (at the least) from attempting.
Thanos has taken to a Smash Mouth approach to combat.
He blasts. He punches. And he relies on his shields/durability to keep him standing.
But he acts on a system of high durability for defense. Not insane healing factor. He is no Lobo.
Sentry, on the other hand, has shown a healing factor that is immeasurable.
Total molecular body control. The ability to rebuild his form from total annihilation.
Virtual immunity to physical damage.
And the ability to reform from death by molecular based damage.
Thanos can blow Sentry apart, and Sentry has Feats (in arguably lesser form) that show he is capable of re-creating a new body as needed.
Thanos can rend his flesh from the bone. Sentry has shown no need for it. He just pulled a Ghost Rider (style) finish on Thor. Flesh damage is looking rather useless.
Sentry can strike Thanos with force that is arguably in the same league as his own.
This is based on compared "Herald Class" combat analysis.
Thanos dropped Surfer in three hits.
Thor has knocked Surfer out cold on more than one occasion.
Sentry dropped Thor in in LESS than three hits.
This shows that BOTH men can drop a Herald/Godling Class foe out in roughly 2-3 strikes.
And BOTh men have yet to find challenge to their strength limit beyond this in their current forms.
So we don't know who is currently stronger. Most assume Thanos. But have no way to quantify it beyond character preference.
And no way to show "how much" stronger Thanos is (if indeed he is at all).
Strength is thus either up in the air, or "may" favor Thanos.
We have durability that seems to favor Thanos. It's hard to hurt him.
And Healing/Reconstruction that HIGHLY favors Sentry. It doesn't seem to matter if you hurt him.
We have a HUGE speed advantage for Sentry.
The guy can move at multiple time the speed of light, and has blitzing Feats much like Superman.
Thanos will hit him. I have no doubt of this. But Sentry, sans PIS, should hit Thanos a plethora of times for each counter strike.
This in turn SHOULD counter much of any "strength gap" between the two.
...looking at the tell of the tape- why exactly are folks screaming for Thanos? confused1
Seriously-
Sentry has a HUGE edge in speed.
Sentry has a HUGE edge in regeneration; seeming virtually immune to conventional damage.
Both have "beyond Thor/Surfer" Class Strength.
Neither have a defined upper limit for their Strength.
And Thanos is not invulnerable. He can be harmed.
Black Bolts voice helped to define the limits of Thanos' durability.
One scream to the face is enough to bloody Thanos up a bit. Minor damage was done.
If BB had pulled out a large song book and started singing X-Mas Carols into Purple Chin's face- Thanos would have eventually fallen down.
That is simple logic based on direct on-panel evidence.
And it proves simply this one vital point... Thanos is NOT Juggernaut.
You "can" beat Thanos into a state of unconsciousness.
But you "cannot" beat down a creature that is capable of simply re-creating itself if you rip it apart.
Or that can rip itself apart just to show you its skull for dramatic effect.
Honestly- why wouldn't Death Sentry take this?