Kaguya's nine tomoe Rinnegan sounds like the most powerful, since it can cast Infinite Tsukuyomi and Dimensional Shifting. About Sasuke's six tomoe Rinnegan and Hagoromo/Madara's purple Rinnegan, I think they're tied.
Kaguya's obviously. Hagoromo's is a devolved version of it. sasuke's is a hybrid of hagoromo's. Its in between kaguya's and Hagoromo's. Sasuke's own maybe more powerful. The fact that he surprised him when he put the bijuus under control with once glance.