Has to be 2-1 to Bronx for me.
Bronx has great Tiger and Snow Leopard exhibits, these are some of the best exhibits for their respective species in the nation. Lions, Spotted Hyenas and African Wild Dogs all have good exhibits. Dholes are a new addition to the zoo and are in the former Polar Bear exhibit, while Brown Bears are in a decent grotto. I don't remember the other exhibits too well, but none of them were bad.
So overall, Bronx has a larger collection, with no real bad exhibits and some really great exhibits as well. Zurich is worthy of a point, but Bronx wins this one.