She hulk is best, her heavy inflicts slow which disables their unstoppable for a reasonable duration... Also as long as cap iw has at least one of his kinetic charges he will automatically negate an unstoppable buff on the opponent... Keep in mind I'm not 100% on the interaction with these with The Thing, as I believe his unstoppable is passive.
Doctor Strange (Woke) has a chance to nullify the Unstoppable Buff Scarlet Witch can potentially nullify it (risky as she has to hit into it, and crit, and have the nullify work)
AA-Ron (Woke) can stack Neurotoxins which reduce the chance of Unstoppable proccing in the first place.
Thor Jane Foster can inflict Stagger with her Heavy attacks which will stop it proccing The Hood inflicts Stagger with critical hits
Luke Cage can transform Exhaustion debuffs into Concussion which prevents it from proccing Quake can not only prevent them from gaining enough power to gain unstoppable by utilising the Quake & Bake tactic, but the Concussion debuffs she can place on them also prevents it proccing
Mephisto's Soul Imprisonment thingee can prevent buffs proccing
Juggernaut himself can inflict Stagger by attacking into their block while Unstoppable
Comments
She-Hulk
Spider-Gwen
CapIW
Scarlet Witch can potentially nullify it (risky as she has to hit into it, and crit, and have the nullify work)
AA-Ron (Woke) can stack Neurotoxins which reduce the chance of Unstoppable proccing in the first place.
Thor Jane Foster can inflict Stagger with her Heavy attacks which will stop it proccing
The Hood inflicts Stagger with critical hits
Luke Cage can transform Exhaustion debuffs into Concussion which prevents it from proccing
Quake can not only prevent them from gaining enough power to gain unstoppable by utilising the Quake & Bake tactic, but the Concussion debuffs she can place on them also prevents it proccing
Mephisto's Soul Imprisonment thingee can prevent buffs proccing
Juggernaut himself can inflict Stagger by attacking into their block while Unstoppable