Protagonist and Antagonist aren't really applicable terms here, but if we must put labels on people, the more conventional way of doing so is probably to call the Narrator the protagonist. Why? Well, first of all, he's the character we know best, we identify with him, and we see the story through his eyes. In addition, the Narrator is the most accessible, comprehensible, and essentially human character here – unlike Bartleby, the Narrator is not alien in any way, and unlike the other clerks, he's not just a caricature. He's the closest thing we get to a real, live human being in this story, and through that basic identification, his quest (to understand and help Bartleby) becomes our own.