Itachi > Tobi

[Orochimaruofthesound]

Itachi and obito knew eachother for a long time, yet obito still managed to keep secrets from him. Obito is just as smart as Itachi...

And anyways kamui is instant, the only reason why minato was able to analyze obito's ability was because he can teleport, so he had some breathing room. Itachi has no such way of creating distance between himself and obito

but pre rinnegan obito has no "known" jutsus that can actually work against itachi

 

[Draphsin]

but pre rinnegan obito has no "known" jutsus that can actually work against itachi

Kamui is all he needs

He also has mokuton for safe measure

 

[bruce lee was uchiha]

itachi couldn't defend kamui attacks forever, he was already close to blind when he fought sasuke. he would definately lose his sight in a fight against obito. on top of that his chakra reserves are way smaller than obitos (thanks to obito leaching off of hashiramas dna via zetsu)
this is a fight, itachi would not win... he even implanted the amaterasu in sasuke's eye to auto fire upon seeing tobi, and an amaterasu to the face wasnt enough to take him down, he seemed basically unphased by it once he got the flames off of him somehow...
sasuke's only hope would be to seal him with the totsuka which.... by the time he'd land a strike with susanoo, he would die of chakra loss/be blind.