To me the true theme is Barbastella. It's not a theme that plays when Batman is in action, during heroic things (the way we tend to think of superhero themes), but it's a cue that pops up in many of the most meaningful moments of the trilogy.
I think everyone has their own favorite cue that they like to think of as "the" theme though.
The piano cue from that is oddly something I LOOOOVED in Begins and grew to dislike more and more in each of the films. I think it got to be too on the nose, if that makes sense.
To me the true theme is Barbastella. It's not a theme that plays when Batman is in action, during heroic things (the way we tend to think of superhero themes), but it's a cue that pops up in many of the most meaningful moments of the trilogy.
I think everyone has their own favorite cue that they like to think of as "the" theme though.
t: