I think it is Jim Gordon
Thomas Elliot used to be Bruce's best friend until the events of Hush. Superman is more of an ally. Alfred is like a father. All the robins and batgirls are more like sons and daughters. And some are his adopted children. Batman has no true friends, but Clark kent would be the closest. They are around the same age and have equal respect for each other, and neither has more authority so they aren't like son and father. But he is still more of an ally
Dick is pretty much his son and alfred his father - that would make it either jim or supes and that really depends on the writer/story.
in the new 52, i think its superman. in the second arc of JL the members was saying how batman trusts no one until supes declared he only trusts him. Also, i think it was the cheetah issue when superman became a cheetah, batman got pretty emotional about having his friend saved.
and also i think aquaman and bruce have been getting pretty close, i like they interactions