Itachi demonstrates the full potential of the sharingan from genjutsu to ninjutsu and he doesn't just spam techniques but carefully analyzes and finds the appropriate use for the sharingan
Tobi uses the sharingan just to get from one place to another.
Sasuke doesn't know how to use the sharingan to its fullest.
Madara's ego prevents him from utilizing the sharingan properly, he just likes the destructive power it offers... you can't disagree with that.
Kakashi not being a member of the Uchiha, can't use it to the full capabilities.
Shisui had great prowess with the sharingan but little is known of his feats.
Obito... well really?
Ik you didn't include Danzo but I just want to add him if that's ok :]
Danzo not being an Uchiha like Kakashi has the same problem and he basically sucks.
So Itachi takes the cake imo.