I have an answer. Edo Madara could win. Itachi and Nagato could also win. Both sides have a lot going for them so I say it is a toss up. When it comes to versus threads with the strongest ninjas it is always a toss up.title says all. Madara combines sharingan, rennigan and mokuton and have an undying body. itachi and nagato have sharingan and rennigan too but are two persons, both can defeat an edo (totsukas sword, human path, souldragon of gedo mazo) and 2 are always better then one.
Madara whether he is Edo or not could in theory beat any ninja in the series. There are also other ninja in the series that could in theory beat Madara. Minato? Sure why not? Itachi? Sure why not? Nagato, Naruto, Sasuke, or any other ninja considered to be extremely gifted could in theory beat Madara.
99% of all versus thread opinions on who would win are purely biased. The simple truth is that no one actually knows except Masashi Kishimoto. Send him some fan mail.