See, most people think he's Izuna or Obito.
My Predictions are basically... "If Tobi has Kamui or a Space/Time warp Sharingan Jutsu."
Obito Uchiha
If he is: The Kamui is Obito's Magenkyo Tech, then he is the only one to use it. Since Kakashi took one of Obito's eyes, he can now use one of...