Board Thread:Versus Debates/@comment-25096344-20160509164213/@comment-5547501-20160510083826

It depends on if Obito can break Itachi's genjutsu. I don't think he was ever shown breaking any, but having been trained by Madara and supposedly having controlled the Mizukage for years, I can't imagine that he could be trapped by simple genjutsu. Tsukuyomi might work as it is a special genjutsu, but I don't think any physical attacks will, due to Kamui. This includes Totsuka and Yata.

Itachi is probably fast enough to dodge or set up countermeasures once he realizes about Kamui, but he doesn't really have any abilities to capitalise on its limitations. So the options are, Itachi wins with Tsukuyomi or maybe Izanami, or Obito wins due to chakra exhaustion on Itachi's part. Both seem unlikely, as Obito won't be caught so easily as he isn't as cocky as Kabuto and probably knows about Izanami, and he also will likely avoid Tsukuyomi as best he can, due to knowning it is Itachi's speciality, but nor will Itachi waste unnecessary chakra once he realizes nothing can hit Obito at a distance.

I'd say 50/50, only because both have strategies that can win, but require a misstep in the other persons behaviour.