the strongest sharingan user.. ?

[Aze]

The Elder Son of Rikudo Sennin ofcourse.

And Rikudo Sennin.


Also Tobi has shown some incredible skills with 3 tomoe only.

 

[Kratos of cruxis]

You cant really pick the best sasuke is the best at ama madara has the best susanoo and itachi best tsyukiyomi no one is better in other sections