madara. this is all of them with their fullest capability of their mangekyo sharingan meaning that all 5 of these Uchihas are capable of perfect susanoo.
So there's no point in comparing susanoo's down to that measure since all of them have one.
Now it just comes down to their primary mangekyo sharingan power, which rules out madara immediately because he doesn't have any.
Leaving Shisui, Itachi, Obito, and Sasuke.
Shisui and Obito's mangekyo are far superior than any Uchihas I've ever seen, without a doubt but it all comes down to who can strike first close distance and long, and that would be shisui because ocular genjutsus are instant. Itachi also follows but Uchiha's can break his Tsukyomi and Sasuke's flame control can manipulate Itachi's amatersu. So Kishi designed mangekyo Sasuke to be able to beat Itachi granted if knowledge comes into play.
I know a lot of noobs immediately say Sasuke or Obito is the weakest because to them it's a popularity contest. But if you actually think and laid out who's capable of what and how they use their skills in battle. Madara loses and Shisui comes on top of everybody else.
Edit.
