I loved Swanson's. HOwever, it's really expensive. It helped me on peds, internal medicine, psych, and ob as well though. it's a question book, with excellent explanations. it's actually for fp residents for their own boards.
I'm going into it, so i went hog-wild with the books. best one: NMS. Best succinct one: First aid.
If you are merely doing "rotations" in EM, I would steer clear of Tintinalli and the other large texts. EM secrets was very helpful and many basic questions. Your EM rotations should have a core article list that they will provide...otherwise NMS would be your best bet.