hahsirama would win IMO
due to bringer of the darkness
what caused nagato to get hit by itachi in the end yes teh blinding of his shared vision caused his reaction time to be low and thus got him killed as seen here
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him being a sensor doesnt mean he can dodge all techs and he couldnt react here as we have seen. And with one tech hashi can make him completely blind he would be completely vulnerable as he was in this state. When ur blind u really would know where to attack or use your powers as effectively.
as kabuto mention here he couldnt dodge that attack due to that and his mobility issue
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as seen here even nagato can be hit with ninjutsu when caught of guard
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and here
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as u can see as soon as hashi uses bringer of darkness nagato is in this vulnerable state and hashi has to deal the final blow and as we have seen nagato wouldnt be able to defend fast enough and wouldnt even know where to attack. All his summons would be useless in this jutsu and hashi can use either mokuton or use his swords as a finishing blow for nagato.
hashi uses nagato biggest weakness against him which is his blinding of shared vision that puts him in the most vulnerable state. An as long as hashi can deliver a swift finishing blow which he certainly can with mokuton or swords hashi would win. and nagato wouldnt know what hit as its the same scenario with itachi but unlike itachi hashi doesnt have to take out eye by eye but just use this one jutsu