Jackson is the standard source. I like it very much, but Schwinger is simply a master piece, and I like. It's full of gems. Alone the treatment of cylindrical Bessel functions with elegant operator techniques is worth the whole book.
I don't like both books conceptionally wise so much. They are both written from a classical perspective. From a HEP/nuclear theoretical physicist's point of view, classical electromagnetism should be introduced as a relativistic classical quantum field theor (and it's in fact the paradigmatic example of one such theory with the clear advantage that it describes a vast amount of observable facts and has far-reaching applications in electrical engineering, electronics, and optics). The best book from this point of view is, in my opinion, Landau&Lifshitz vol. 2 or Scheck's Theoretical Physics book vol. 3 (I'm not sure whether there's an English translation of the latter, but the German edition is great).