Itachi by far, because he was never powerful, he was all hype, and the only reason seemed powerful is mainly due to the aura that surrounded his character,and because of his popularity.
For example, itachi's basically the basket player who could only win if the other player was blind, missing a leg, or in a wheel chair. He continues to beat people like this his most of his career and a bunch a morons start praising him like hes the best for it until one day he gets challenged by a real player. However, itachi showing his true coward nature only accepts the challenge with the stipulation that only he is allowed to use a team, so now its a team vs 1 affair,and when itachi and his WHOLE team win by the skin of their teeth he's the one praised as though he did it by himself all because of some sob story with his family.
the funny thing that as you said he didn't fight someone with full power without being crippled
and controlled ( through edo tensei ) like Nagato
or someone who doesn't has a counter for genjutsu like kakashi part 1
also he is the weakest uchiha in term of chakra and stamina
noticed when he met jiraiya and gennin kids after using amatersau he retreated and kisame asked him why he said i need to rest
so he is the type of person who can't take long fights and wanted to end the match as soon as possible with genjutsu because he is lacking the stamina since he doesn't has EMS
he himself admitted that Sasuke has more chakra and stamina
also Orochimaru cleared this
him as an edo with
unlimited Chakra couldn't take down Kabuto by himself
and needed Sasuke MS help with Sasuke's susano and still got caught in Kabuto genjutsu
and guess what it's a genjutsu actually from a genin ( tayuya )
how can someone called by his fans the master of genjutsu caught easily by a non genjutsu type of character ?
also when kabuto cut him in half , if he wasn't edo he will be dead !
until he pull off some nonsense called izanami
kabuto was toying and didn't even use edo tensei against him and get benefit at least from one body of his arsenal
so it will be a fair fight Edo uchiha + Sasuke VS Kabuto and an Edo
yet you see his fans still think he can defeat the likes of Tobi , Madara and pain
when kabuto himself shat on his pants when he saw Tobi and used edo tensei immediately
my final take on this
is that since Itachi is the master genjutsu user as his Fanboys claim to be
i guess they're still in his Genjutsu and maybe for eternity lol