Either Genealogy of the Holy War or Path of Radiance. Genealogy had an epic setting, great world building, politics, interesting gameplay mechanics, a more mature and complex story (for a Fire Emblem game, at least), low difficulty, cool characters, amazing soundtrack and replayability. Path of Radiance had great writing, decent graphics, great characters, great gameplay mechanics, low difficulty, good plot and some replayability.
I also liked Thracia 776 for most of the reasons I liked Genealogy, and Shadow Dragon because of the superb writing.