Sorry man i gotta disagree, i mean Shisui Uchiha would be able to control Itachi which would make HIM the strongest. Plus Itachi's breaking free of Edo Tensei was down to Shisui & Luck.
Its very hard to say who is the strongest shinobi of all time as they all excel in different areas. Minato was increadibly fast while Tsunade can demolish a battlefield with a stomp. It really comes down to situation and who your opponent is, throughout the series people like Kakashi would say things like "im a bad match for you" because his abilities happen to be high in the area his opponent is weak.
Itachi had a powerful genjutsu and ameratsu + Susanoo
However he has only been shown to be able to cast his genjutsu on one person per time, which means he would be left open for attack
(Uchiha are strong 1 vs1 but not when its 2 vs 1)
His ameratsu was supposed to be unavoidable, but people have done so several times now. Its definately a killer if it gets you on the flesh but on the clothes the person can simply remove the garment and be fine. So this is weak against very fast opponents
Susanoo is very strong and has his special weapons for Itachi too, however Gara has been able to pull someone out of it with sand and Kabuto has proven it is weak against noise.
Itachi isnt perfect, he's just very good.
So im afraid i cant award him best shinobi of all time, he may be one of the best but not the best by far.
