The Uchiha clan is supposed to be descended from the Older Son of the Sage of the Six Paths, while the Senju Clan is descended from the Younger Son.
As the Older Son he had inherited the eyes of his father's IE: Rinnegan. Not only this but he felt that power was key and domination is a form of power.
Further Tobi made comments that an older brother could not kill his younger brother (He is one of the few key figures in the universe with a brother). And his claim that the Rinnegan were not Yahiko's implies even more so that The Eldest son of the Sage is in fact Tobi.
Good point, but don't forget Shisui Uchiha
. Who lost both of his eye (and could also stole Obito's eye in the battle of bridge.
He is 1 of the best ninja of the clan during his time. Tobi and his intangibility, Shisui and his body flicker tech, a high-speed movement technique, allowing a ninja to move short to long distances at an almost untraceable speed. Not to mention Shisui's Genjusu can manipulate and control an enemy, just like Tobi did to that one Kage.
Why I don't think Obito can be Tobi ? Shisui Uchiha is old enough to have been responsible for the attack on Konoha. Minato confront Tobi once during the awaken of 9 tails, Obito would still be a kid, not a grown up.
p.s: Just my 2 cents. I used to believe obito = tobi. But after reading stuff about Shishui, my belife that obito = tobi is 60% less