Pein Invasion, Land of Waves, and Tsunade arcs. Those personified the story's awesomeness and were all around amazing arcs. If I had to choose between those 3, it would be the Pein arc.
Invasion of Pain - grief, destruction, that Sage Mode entrance, appearance of Minato, rinne rebirth, Naruto's acknowledgement by the village. It had it all.
I am hopeful that the final arc will surpass it.
Completely agree. I loved this arc, and for some reason I am doubtful that the final arc can surpass it with the turn of events we are seeing.
The pain arc (PIA) was full of amazing emotions which would be difficult to recreate - Naruto's amazing sage training, Naruto's realization of his love for his parents (his "two suns" *_*), Minato and Kushina (<3), Jiraya's significance as a father figure in Naruto's life and as a prophet, Naruto's peak of his protagonist existence with amazing powers & unparalleled TNJ, his final acknowledgment by the village, Sasuke's newfound love for his dear brother and will to find himself, Itachi soloing... you know it just cannot get better than that!
What can the final arc do better? Can it surpass PIA's development of Naruto's relations with his parents? No... Can it truly show Naruto as the hero of the show, like PIA? Maybe, but with all these "asspull" power-ups, it is getting doubtful... Will it have Itachi, the solo king? Probably not... Will it have more on Naruto's childhood, Iruka, and more actual training like he did on Mount Myōboku? No, doubt it. In short, there is little on which you can improve on from PIA, apart from maybe the Naruto-Sasuke relationship, and maybe the Naruto-Sakura relationship too.