Minato had potential but hardly accomplished anything during his tenure except die protecting it
Hashirama founded the village and defined the role of hokage, much in the same way Washington defined the role of the President for generations to come. It was Hashirama that created the concept of shinobi villages; it was hashirama that brought the nations together if only temporarily and passing out the power of the tailed beast he'd captured as temporary peace offerings. In terms of power, Hashirama had only one equal, Madara, and even in that case he was the greater shinobi, not by much but enough to win when it counted and that's all that matters.
Tobirama, inferior to Hashirama but alot in terms of power; but he still was far greater than mostly everyone during that time of war and during his reign as hokage. It was Tobirama who created the details of structure of the village, filling out the details of the vision Hasirama had but his lack of details left Tobirama to fill in the void. He also created alot of powerful yet essential jutsus. Also helped train and bring up Hiruzen Saratobi, who turned out to be one of the greatest shinobi himself. Tobirama's only fail, also his biggest, was his attitude towards the Uchiha. While extremely practical in his reasons for putting the Uchiha exclusively on the Police force it was also the seed that lead to all the contention with the Uchiha & Konoha down the road. Essentially cutting the Uchiha out of the political scene in Konoha and out of the major decision making of the village
With Hiruzen Saratobi, in his prime he was compared to Hashirama in terms of power and strength, which is a major accomplishment. Being revered as a god says alot. During his watch, just as the 2 hokages before him had, Saratobi ensured the the village remain protected and standing strong. But unlike his predecessors, he managed to do it without dying so young, but lived well past retirement age. He saw the Konoha successfully through 2 Shinobi World Wars and kept all enemies at bay with the exemption of Orochimaru, who just loved starting war for the sake of it. He brought the village together to the best of his ability; always seeking peace and caring for all like his own; the ideal started by Hashirama & Tobirama. His only failing was keeping Danzo around