If you have no choice to read just one of those two titles: Batman & Detective Comics, which one should it be ?
For me, it's Batman.
I think Snyder is a fantastic writer. He lives and breathes making Batman a detective story and incorporates a rich history of Gotham I haven't seen before. It actually takes me time to read it because I want to soak in the words and not miss anything, unusual for a comic these days.
Greg Capullo is also hands down one of the best artists out there. Amazing steal from "Haunt."