There are so many insane people on this thread who know almost nothing about genjutsu or Itachi or even Naruto as a whole.
Someone said Jiraiya was a master at countering genjutsu. FALSE, he himself said he was terrible at genjutsu.
Tsukuyomi only takes one second real time, not enough time for anyone to break out of it even if they could. Itachi said that only a blood relative of his with the sharingan could break out of it. He is a genjutsu master so don't you think he knows ways to counter genjutsu? ANSWER - yes he obviously does, anyone who thinks otherwise fights the manga and what is written there.
Hashirama and Madara - We know literally nothing about his fight with Madara or how strong he and Madara were back then. Who cares if Madara had EMS? Itachi was likely more skilled than him in using it because as Itachi has showcased in literally every battle he is extremely talented. Kakashi said that legends of the past are always overstated and I am inclined to believe him. Hashirama didn't fight the fox he suppressed it and it was sealed into his wife, there is a difference. Would you say that Yamato fights the fox? That is what Hashirama does as mokuton is how they are similar.
Since we know nothing about Hashirama and I don't see any counters to Tsukuyomi or Amaterasu then I'm going to believe that Itachi beats him out.
Now on to Itachi. There are haters on this site who hate just to hate, they hate all of the overpowered characters. Itachi and Minato being the favorites to hate on for that group.
Now let's take a look at Itachi's abilities. - Can copy jutsu, track and predict movements, see chakra, has both fire and water affinities, is one of the fastest characters in the entire manga (fast enough to get behind Bee before he could move, and fast enough to dodge Naruto's attacks in Rikudo Mode), incredibly smart, has three OP mangekyo sharingan abilities: Amaterasu, Tsukuyomi, Susanoo each of which is devastating and easily one of the highest caliber jutsu of their types. And he is a normal genjutsu master, being able to counter a genjutsu specialist (kurenai) and put her under a genjutsu.
Now I will admit that there are a few people who can probably beat him but that is because of one of his only faults, he has pretty average chakra levels, and eventually he would go blind. And of those few people that would probably beat him, he is always in the running, you can never discount Itachi from winning a fight.
People that have a chance to beat Itachi:
Minato
Nagato
Madara (current)
Maybe Bee, unlikely but because he can break out of most of his genjutsu then that could turn the tide.
Naruto (only if the fox ever helps him, otherwise Naruto is incredibly weak in genjutsu)
Sasuke (current, only Itachi's eyes could help him beat him, which he wouldn't have)
What most people fail to realize is that only one person in the entire Naruto universe has a counter to Tsukuyomi (Bee has the hachibi and Samehada) and that even that might not be enough as Tsukuyomi only takes one second real time. If genjutsu is used only Bee, or if the fox starts to help him Naruto, can break out of it.