My favorite OP would be the Baccano! OP:
The Jazz is perfect for the 1930s era that they are (usually) working with in Baccano! and the fact that it introduces all the characters helps to keep all of the names straight. Additionally, it even plays with some stuff that is in the LNs and not the anime as a nice tribute and sneaks in a few details from the series that you may not notice on your first viewing ^.^
Hacking to the Gate from Stein's;gate and the OP of Durarara get honorable mentions ^.^







