I say it's TPatF. It showed Disney returning to their roots with the fairytale musical -- traditionally animated, no less. And this next point is more subjective, but I think this is the one that got people specifically talking about Disney again. Meet the Robinsons and Bolt don't exactly strike you as "Disney films," but this one sure does, and it sparked discussion about how the studio is back and even the fact that it features the first African American princess.

This one marks the returning of Disney since 2000s where most of their films are flopped.

Why did you add Meet the Robinsons and Bolt on the poll, when they belong to the Disney Post Renaissance era?
In reality, the Revival Era began in 2009, with the Princess and the Frog. While I did like a lot of movies from the Post Renaissance era, not many of them were box office hits, and some of them just bombed. Also, it had two of the worst Disney movies I've ever seen: Home on the Range, and Chicken Little. Although, I do appreciate it for being a very experimental era, that at least tried to do something different. Much as I love the Revival Era, it would be nice that they would deviate from the usual. However, being experimental won't mean success. Doing a "Revival Era", where they would try to bring back the classic Disney style and feel is the best way to go.

^Because many peoples don't know that Meet of Robinson and Bolt aren't count as Revival Era as well, and it's debateable between Disney fans.

Earliest

This one :)