In my opinion that's way too abstract a fight to make a detailed argument about.
I expect Itachi to have fundamental knowledge of Tobi's Kamui, similar to Konan, but he apparently didn't know of his Izanagi, hence the failure of the Amaterasu trap. Tobi on the other hand should have pretty extensive knowledge of Itachi's abilities, with only Yata, Totsuka and Izanami being questionable.
Hype is kind of disregardable, here. From what I recall, Tobi had an incredibly high opinion of Itachi and knew how skilled he was, while I think it was implied Itachi was weary of Tobi and avoided facing him directly, but that was under the impression of him being Madara, which implies a lot more strength than swirly-mask Tobi actually had.
Argument for Tobi:
Tobi's onyl way to win is by absorbing Itachi. Amaterasu is an effective counter to any absorption attempts, but only as long as Izanagi isn't active. As soon as that's the case, Tobi could try a brute-strategy similar to Danzo, tanking any damage (even Amaterasu) just to be able to absorb Itachi. But then there's Susanoo's instant activation speed, and being crushed to the floor would definitely stop the absorption process. Tobi's absorption was hinted to also work instantly or at least accelerated after he failed absorbing Minato, but I have yet to see proof of that. So Tobi's best shot would be similar to Danzo's, trying to wear Itachi out by forcing him to use straineous MS-techniques. I don't consider Tobi's small-scale usage of Mokuton any threat, considering Itachi's speed, agility and Susanoo.
Argument for Itachi:
It's vice versa, Itachi's only way of harming Tobi is Amaterasu, but that only until Izanagi is used. He'd have to try and wear Danzo's Izanagi out, which I cannot see happening with only MS techniques having the potential to actually harm him. Itachi has, however, a pretty good shot at defeating Tobi with Izanami. Once he's in Izanami-trance, Itachi is free to murder him any way he wishes. If Tobi opted for a brute Izanagi strategy, forcing Itachi to continuously use Amaterasu, I could very well see the latter recreating a physical sensation twice and thus activating Izanami without seeming suspicious. It's Itachi, after all.
A case could be made for either one, but since Izanami was created solely to punish Izanagi-users, I'll follow this satisfying storyline and give it to the one and only solo-king. I do, however, consider Tobi to be overall stronger, since his mix of techniques is pretty damn OP and makes him invincible for most people, especially pre-war.