While not always true, heroes are frequently defined as much by the villains they clash with as anything else, and the villain and their machinations frequently serve as the thing that grounds the journey of the hero and makes it feel like a journey rather than aimless wandering, the villain's defeat often being the ultimate goal.
Guts' whole story in Berserk is centered around his desire to get revenge on Griffith for destroying the Band of the Hawk. Midoriya's becoming the "greatest hero in the world" is inexorably intertwined with his conflict with Tomura Shigaraki and the latter's desire to tear the world down. Amuro Ray's legendarily messy rivalry with Char Aznable remains one of the most famous in the medium of anime to this day.
Put shortly, I'd pick the villain.