The 1st as stated by tobi during his chat with sasuke about the senju uchiha history was the strongest ninja of his era. Note the his era part. The first was the most feared and known ninja in his time. Even now his name is know to all villages and ninja's of this current era. In terms of who did what, the 1st created the village system that would later be adopted by the other lands. He came up with it and offered a treaty to the uchiha in the process, which they accepted. He passed out the biju to create balance among the nations and as tokens of freindship. The fourth just sealed the 9 tails. You can't compare their accomplishments because the 1st did far more for the ninja world then any other ninja or character ,aside from ninjutsu's originator. The sage wasn't a ninja, he created the ninjusho sect that would later become ninjutsu. As far as who is the most powerful I'd have to say it would be a tie. Each one has an advantage over the other but its not enough to say without more proof of skill which is the greater fighter. The first is said to have herculean strength on par with tsunade's. Both married uzumaki so its unknown if the 1st also picked up some sealing jutsu(manga shows him with a big scroll with a seal on it though). For the record the 1st's wife is the one who dealt with the 9 tails. She sealed it inside of herself and this was confirmed by kushina during her talk with naruto during his battle for control over the kyubi. We do know that the 1st was a master of all forms of jutsu because he wrote the scroll of sealing which contained some of the most powerful jutsu in the village. In the manga and anime the third hokage is stated to be stronger then both his predecessor and was nicknamed the professor for mastering all the jutsu of the village. As gifted as we was the fourth was known as the greatest ninja the village has ever produced. I have personally seen this interview as I subscribe to shonen jump here in the states. I don't have that issue anymore but it is something that was part of it. You have to give credit to the fourth for his flying thunder god. So far no one who we've seen come up against it has won. he beat tobi with it, and he fought to a stalemate against A, B, and his squad by himself. Its safe to say he could have stabbed B and teleported away before B could stab him or he could teleport and come back later since he was tagged. The thing that makes the fourth so strong is that jutsu. Many of his jutsu revolve around it and in battle is has been tested. Hashirama defeated the strongest of a clan but the fourth took out an entire battalion of ninja in a flash. If both used sealing jutsu its not to far of a stretch to say it would actually be a stalemate. From what I've seen no jutsu compares to sealing jutsu, except the sages creation of all things. I'd say tie until we see other wise. Maybe the additional footage from the new movie will show this fight.