Depends but it's highest is definitely a 10/10
Even though Sasuke susanoo got destroyed many times by Kaguya it counts compared to somebody like her.
Also it depends on what you mean.
As far as susanoo go it's great, but in my opinion it should determine weather or not how hurt the user gets while the susanoo gets destroyed. Like people say Kaguya destroys Sasuke susanoo, correct. But it doesn't matter if it's "immortal" and sasuke didn't get harmed just blown away susanoo... and seeing how strong madara was vs 8 gates I'm sure in terms of jutsu those were powerful asf.
Susanoo goes up to 18-20 in my opinion because the power scale is huge with Kaguya/Guy/Lee/Naruto/Sasuke