Looking back at all the context, it seems Hashirama was the stronger of the two in general.
Hashirama stated that Pre-EMS Madara had wanted to "erase me (Hashi) from his (Mads) life". And that he and Mads fought each other day after day, but also stated that "I (Hashi) had never abandoned our (Hashi × Mads) dream (Konoha)" sorta implying he was holding back all those times.
And during the battle where Tobirama fatally wounded Izuna, Hashirama stated "Madara, you cannot win against me". Which seems kinda boastful but may be true since Hashi at this point would have a proper gauge of Pre-EMS Madara's power. He also asked Madara to join the two clans so that the conflict, the warring states it seems, would eventually stop due to the strongest clans joining.
Then appears EMS Madara, after Izuna's death, who went on to fight Hashirama again. End result is "Madara's back touched the ground for the very first time", "at the end of a battle that lasted a whole day". Hashi still seemed to have held back because he still wanted that whole "making a village with my bff" dream with Mads.
After making a village with Hashi, Mads goes on another villain spree and stated to Hashi, "You're the only one who's an even match for me", and "I'm looking forward to the battles we'll fight". Which is something reflected in his entry in the 4th Databook;
Madara’s hatred was split between (two entities): Hashirama, because of his incompatible dreams, and also towards the village of Konoha. He then unfolded [incidents] upon Hashirama by attacking the village on multiple occasions. In a battle to the death, and with Madara’s defeat, the curtain closed [on that era]. However, that was the rise of the curtain for a great dream. Madara escaped death. Cutting apart the fate of love and hatred, he aspired to a world even without winners or losers. As for Madara, reality was certainly Hell. At the end of his lifespan of sorrow and anguish, and at the moment where his life was about to collapse, Madara finally awakened the 「Rinnegan」. It was dwelling in Madara’s pair of eyes: the power to change his dream into an ideal reality!
Implying that Hashirama beat back EMS Madara multiple times until Madara brought Kurama along to the fight.
Though, a section in his entry does say this;
They are equal in strength. Madara remained unchanged, but Hashirama changed for the sake of the village. A paper-thin difference [between the two of them] decided victory or defeat
Note, that these translations come from Narutoversity.