Which genjutsu is stronger kotoamatsukami or tsukuyomi?

What power of Mangekyo Sharingan does Itachi have?

Mangekyou Sharingan users have three abilities. Two unique in both eyes and Susano'o that can only be used when you have Mangekyo Sharingan in both eyes. Itachi had Tsukuyomi on his left and Amaterasu on his right. Sasuke had Amaterasu in his left eye and was able to extinguish and control the shape of the flames in his left eye, as he did during his fight with Killer B to prevent B from being killed by Amaterasu. Obitos Mangekyo both used different shapes of Kamui, the left one he gave Kakashi could use a long-range shape that could teleport objects into the Kamui dimension within the user's line of sight. The right one he kept could only teleport himself and people with whom he had physical contact into the Kamui dimension. It also enables the user to become immaterial by teleporting the attacked parts of themselves into the Kamui dimension. The full extent of Shisui's abilities is unknown, but both the eye Shisui gave Itachi and the eye Danzo took could use Kotoamatsukami. Madara and his brother's abilities have not been revealed, but we do know that Madara was able to use Susano'o, which means that he unlocked the power of his two eyes.

Amaterasu and Tsukyomi are however no generic Sharingan powers. While Sasuke had Amaterasu like Itachi, I believe this was because they were closely related, rather than because it was a generic force since no one else Mangekyo Sharingan users have demonstrated the ability to use Amaterasu or Tsukuyomi other than Madara who uses Infinite Tsukuyomi, but I think it's safe to say that this is a special case because Rinne Sharingan is on his forehead.