Which Sharingan ability is best for defeating MCU Dormammu?

Tsukuyomi probably because it's time.

Any..........?

Koto is your best shot.

I dont think the Izanami loop will do much of anything to him due to the sheer nature of it, Izangi needs a user. 3 tomoe genjutsu depends on the user as well but compositely speaking that and any other Genjutsu oneshot.

SoT oneshots. Kamui oneshots, Ama oneshots. I mean.....

Any of them. Dormamu is fodder to any relevant Uchiha.