Let's break it down.
MOTIVE:
Obito....he loved konaha and willingly gave his eye to kakashi because he ones be was dead.
Fugaku....he HATED the konaha elders and the senju. He was planning on killing them.
Izuna.... He willingly gave his brother his eyes so he could lead the uchiha clan, and then the uchiha clan turned on Madara and disowned him. Which probably pissed Izuna off.
KNOWLEDGE:
Obito....was only 12-13 years old. Was probably never told about the hidden uchiha room which contained the tablet left by the sage of 6 paths. Sasuke didn't even know, and he was the son of the leader of the uchiha clan.
Fugaku....as leader of the uchiha clan probably had access to all uchiha clan history, and all the forbidden techs (including Izanagi which tobi used)
Izuna....almost as strong as Madara. He unlocked MS and since his brother was leader of the uchiha, he probably had access to the forbidden techs and the secret uchiha room.
SKILLS:
Obito.... Barely unlocked his sharingan by 12-13 years old. Dies the same day after being crushed by rocks. Proably knows very few jutsu, especially sharingan jutsu since he only had a sharingan for a hour.
Fugaku: powerful enough to become leader of the uchiha. He probably had access to all uchiha techs, and he was leader of konahas police force. He probably had tons of experience capturing rogue ninja and battling ninja who tried to hurt the village.
Izuna: awakened ms, practiced with madara his whole life constantly improving his skills against the strongest uchiha ever.
Timeline relevance:
Obito.... If he didnt die during the war he would have been 14-15 years old when Tobi attacked konaha, yet Tobi was as big then as he is now meaning he was done growing. Humans grow well into their teens, and continue to grow until about the age of 20.
Fugaku....was an adult when Tobi attacked the village, but was missing at the time of the attack.
Izuna....if he was still alive during the attack on konaha, he would have been an old man. Possibly near 100 years old.
Add all that up and I believe Fugaku is the most likely, with Izuna being second and obito no chance