I always feel like it's a coin toss between Begins and Rises because on one hand, I do think Rises is a more epic and ambitious film, but on the other hand Begins deserves a ton of credit for kicking this whole thing off and setting the tone for the trilogy, not to mention inspiring other franchises. The whole idea of hard rebooting a major film franchise was unprecedented at the time.
I think in the end I look at Begins as a bit of more an "important' movie in terms of its larger impact, but I lean towards Rises because I think it told a really powerful story and helped turn the trilogy into one coherent larger body of work. And also I think Bane and Catwoman add a bit more comic book-y cool factor and fun to the proceedings, even though Ra's is a fantastic and super quotable villain.