I don't need to quote your whole thing just this one : "The only chance would be Tsukuyomi but with six Pains losing one would be nothing when Hell Realm can bring back the dead."
I said this about 2-3 times already. Itachi's tsukyiomi affects the vision + all pain's visions are linked = nagato would be trapped in a genjutsu, along with all of his bodies. That alone should guarantee itachi the win
EDIT: Fine, one more quote just so that you have more thing to counter me with.
"Notice that when ever Itachi uses genjutsu he has to stay still." - Itachi's tsukyiomi lasts under 1 second so he doesn't really need to stay still for hours.
i agree with you, although pain is my all time favorite villain, i still believe itachi would win. everybody here needs to stop hating on that fact and start putting the reality into these discussions... itachi plans out everything down to the persons last breath. we all saw and heard perfect examples of this. im not going to reference manga chapters or pics of them, if you dont beleive the following look it up.
madara praised itachi's way of planing as perfect, he stated that everything and every step of te way he had planned it all out for sasuke. even in their final battle he plotted the whole thing down to him ridding sasuke of orochimaru and dieing at his feet and also giving him his ocular powers.
even that night he had planned it so sasuke would be overcome with sadness and hate towards itachi, giving sasuke the push he needed to keep getting stronger to beat itachi. even again he had shown up and had to inflict more pain to sasuke to show him he still needs to progresss further.
back to the pain vs itachi
pain had many weaknesses. each one could only do one thing and they could be taken down easily if seperated... if itachi could hit any of the pains with the amaterasu it would be over really fast, especially if he takes out the one that uses the giant mouth thing. then after that the rest are childs play... the summoner would be destroyed by itachis susano, plus also the one that uses the mind reading jutsu. the one that absorbs chakra and the one that has the rockets would be destroyed after he uses the tsukyomi on them, the last pain(yahiko) would be defeated by itachi easily due to the fact that he suffers an interval between each attack which can vary to high amount of delay times, especially if he try to almighty push itachi while in susano form... all we would see is pain using the tech and itachi blocking it with the susanos shield the moving in for the kill... either by amaterasu, susano, tsukyomi, or some other tech that he may be saving...
i know pain has his planetary devastation, and his universal pull and i chose not to mention them because they are pointless against itachi, especially if he can turn into crows to avoid the pull from working, and the susano would just bash the giant rock or ground or whatever that pain throws at him outta the way. Itachi was sick when he fought sasuke so, id imagine him being a hell of alot stronger than before plus he gave naruto some of his powers just before he fought sasuke... that if need be those powers would be enough to defeat sasuke, so he gave up alot of chakra to naruto.... so when it would come down to it itachi would have a 90 percent chance of winning.