The Lich. He is way too hard to kill, and even if he dies, he can possess either of them. He can superimpose himself on concepts like Death itself. Sukuna and Mahoraga are not as abstract, and it would be even easier to possess them.
Plus, neither of them have any resistance to his words of power. Mahoraga could adapt but that takes time, and he would get enslaved by The Lich meanwhile. In which case Sukuna has to fight both of them.
The Lich. He is way too hard to kill, and even if he dies, he can possess either of them. He can superimpose himself on concepts like Death itself. Sukuna and Mahoraga are not as abstract, and it would be even easier to possess them.
Plus, neither of them have any resistance to his words of power. Mahoraga could adapt but that takes time, and he would get enslaved by The Lich meanwhile. In which case Sukuna has to fight both of them.
I mean, one could argue that Mahoraga can eventually adapt to the Lich's words of power (which have a similar effect to Cursed Speech, essentially), like Atem said, but Mahoraga (and Sukuna) still get incredibly stat-checked given the planet dicing feat performed by a random Citadel prisoner that the Lich scales to.
In other words, Mahoraga (and Sukuna) get hit with this as the Lich vaporizes them with a blast of fire and calls it a day.