Pre-rinnegan I'm certainly taking Itachi. Obito's genjutsu is talked up too much, I have yet to see any evidence he can stand up to Itachi's crazy levels of it... and Izanami is not only a counter to Izanago, but an out and out way to victory (byt the time Obito escapes, assuming he can, Itachi will have killed him). Itachi is portrayed as such a genius, I'm thinking he finds a way. Remember also that all Itachi needs is a single touch too, as he's got a one shot etheral sword, so it's not like Obito can easily risk contact with him.
Rinnegan Obito has some more tricks, and can probably spam Itachi into submission with the aid of his 6 paths and various other cheapness (though I'm a bit unclear exactly how much of the Rinnegan powers Obito can use, given we haven't seen some of them yet). I'd give Itachi a chance in this fight too to be honest. The Edo Tailed hosts still have no counter to his best techs, so they'll be going down pretty quick.