I don't see how Itachi could even remotely come close to beating Obito. You have a guy with the Rinnegan, arguably the strongest Mangekyou Sharingan abilities, Wood Style and over a decade more experience then you have a guy with a, arguably, 'mediocre' Mangekyou (It's much much easy to counter or deal with than other Mangekyous and has little application to combat beyond casting it) and a toolest built around practicality and teamwork. Itachi is definitely a strong guy and his Susanoo is a great addition to his power but I don't think he can even come CLOSE to handling the guy that controlled 7 of the 9 Tailed Beasts at the SAME time as well as six Jinchuriki combined with the insanity that is Kamui and Obito's own ruthless mindset.
Now if we change the matchup to Tobi, the match becomes much more interesting but I would still have to give it to Tobi. The guy has Kamui (Which he can spam due to Senju genes whereas Itachi can not) and is more than willing to use Izanagi. To add further, Tobi was already more dangerous and powerful than Pein was (and perhaps Nagato) considering as a child he went toe to toe with the Fourth Hokage, controlled the nine-tails, aided in the Uchiha massacre, slaughtered an entire army of ANBU as a kid, etc. Let's put it this way, Tobi killed a S-Class Kunoichi who prepared for, what seems to be a decade for her fight with Tobi and she used BILLIONS of paper bombs and STILL lost. This is the same woman that trained under Jiraiya of the Sannin, the love interest and friend of the guy who (to my memory) founded the Akatsuki and lead his friends in war and is also the right-hand woman of god incarnate, the guy that took Killer Bee, Naruto and Itachi all at once to defeat and Tobi crushed her throat.
To add further, Tobi directly maniuplated and used Nagato and Konan for decades for his own agenda and knows practically everything about Itachi whereas Itachi understands very little about who or what Tobi actually is. So yeah, the guy that fought the fourth hokage at the age of what, 14 (when Minato was practically equal to Itachi as a prodigy) and controlled the Kyuubi? I'm pretty sure he would win.
There's also that minor part where, if I wanted to, I could be a dick and add in Wood Style, Obito was a freaking prodigy at using it as a kid (To the extent that the combination of Wood and Kamui slaughtered an army of ANBU). I don't think Itachi comes even close to having a way to handle a guy that can phase through everything AND use Wood Style.