The only ones I am kinda sure of are that
Himejima is the strongest.
Shinobu is the weakest.
@Zara
Now the rest are tricky.
I love Uzui, but I think he's at the lower half of the list. Mitsuri too.
Rengoku goes in the middle too imo. With a mark he'd be top 3 I reckon, but he died too early.
That leaves Sanemi, Muichiro, Giyu and Iguro.
So maybe something like
Himejima>Sanemi>Iguro/Muichiro>Giyu>Rengoku>Uzui>Mitsuri>Shinobu.