it's obviously itachi. They already said he studied the uchiha lineage thoroughly when he was a kid and knew lots of the secrets. He even MS read the uchiha tablet. Itachi's used tsukuyomi, amaterasu, susano'o, izanami, knew of izanagi, etc.
If it's not itachi, it's madara, but all evidence leads to itachi. It can only be sasuke if he got all of itachi's skill.
Honestly I say Itachi. Having the strongest eyes doesn't make you the best. Madara hardly uses it so the verdict is still out on him and Sasuke uses it way too much. I liked when Itachi used it b/c it was done in a strategic manner versus one like where Naruto spams shadow clones and rasengans.
Madara - More knowledge experience no brainer.
Itachi - Knowledge him having both eyes put him over Obito.
Shisui - For KA and both eyes probably had susanoo.
Obito - Trained by Madara but lacked both his eyes to get the full potential.
Sasuke - EMS otherwise he'd be lower as he is oblivious to a lot of things of the sharingan.
Izuna
Kakashi/Danzo
Danzo/Kakashi these two lack the Uchiha bodies imho are the lowest.
All just my opinion. Although I feel Madara as number one is a no brainer. O_O