The Day-1 DLC's quest is short, and not very interesting. The squadmate on the other hand, is. He also has a lot of dialogue in various cutscenes on other missions.
Diana Allers doesn't seem to have alot of dialogue, but you can have sex with her. Dunno if she has more after you do, I passed up on it.
EDIT: On that note, all the NPCs on Normandy have waaayyy more dialogue than they did in ME1 or 2. Including dialogue with each other, as opposed to just with Shepard.