Its kinda really hard topic.
Lets see.
In case of indra and ashura transmigration it seemed as it was gradual, growing in effect with time because neither sasuke not naruto were busting anything comparable to those freaks till late game.
Even in case of madara awakening rinnegan, he too had to master shit and wasnt all powerful like hagoromo.
In case of invasive transmigration like hago and MC kids Obito/kakashi, one can get better results.
Not to mention that Hashirama and Madara seemed to be the purest forms of Ashura/Indra.
Sasuke - Could never fight anyone alone. He always had constant help, whether it be the Curse Seal from Orochimaru, Itachi, Team Taka, and/or who-ever else was with him during the manga. The only real time Sasuke seemed like a true heir to Indra, was the Revolution chapters in which he gained Rikudou powers, so he really didn't need anyone's help.
Naruto - Well the reason he is not the purest form of Ashura in terms of power, is because Hagoromo split the Juubi before his deathbed. Knowing that much, Ashura was obviously not a Jinchuriki. His power manifested through hard work and cooperation, much like Naruto, but his power source came from his father. --- I know this is a weak excuse. Though, Naruto is probably more like Ashura or at least on the same level of comparison to Ashura as Hashirama, I still believe Hashi is the better option.
Madara - He followed with his own set of rules when he became a full fledged shinobi. I could go on about how he is exactly the representation of what an Indra transmigrate it supposed to be, but to clarify, his clan betrayed him. So in turn he became alone, and decided to go on his beliefs
alone. No one helping him but himself (minus his brothers eyes, even though it's stated in the manga that the EMS holds the other person's power too).
Hashirama - Much like Ashura, he found power that blossomed (Wood style) through cooperation and hard-work. I could go on much like Madara, but it is obvious Hashirama is not a spiteful man, and he always thinks of peace an harmony. Even at times of war Hashirama tried to be equal and cooperate with the other villages that took example from Konohagakure, so in turn he captured the Tailed Beasts and split them evenly among the five nations.