I don't count myself among Sears's legions of fans and Hartwig hasn't gotten to the battle itself yet, so we'll go with Murfin. Originally published during the Centennial, this groundbreaking study set the bar for Antietam studies and inspired a new generation of scholars and enthusiasts alike.2. The Maryland Campaign of September 1862. Volume 2: Antietam by Tom Clemens (2012).
Antietam veteran Ezra Carman diligently assembled a mountain of firsthand accounts of Antietam and the Maryland Campaign as a whole, and his narrative and maps form the basis of their modern interpretation. Clemens is in the midst of completing his own epic editing trilogy of the Carman manuscript, with Volume 2 covering the Antietam battle (thus its inclusion here).3. Unfurl Those Colors: McClellan, Sumner, and the Second Army Corps in the Antietam Campaign (2008) and Opposing the Second Corps at Antietam: The Fight for the Confederate Left and Center on America's Bloodiest Day (2016) by Marion V. Armstrong.
The Armstrong volumes go hand in hand (they examine roughly the same events, alternating side and perspective), so I've included them both here. Together they offer perhaps the clearest and best account of the series of collisions (after the Hooker and Mansfield assaults were spent) along the Confederate left and center.4. The Maps of Antietam: An Atlas of the Antietam (Sharpsburg) Campaign, including the Battle of South Mountain, September 2 - 20, 1862 by Bradley Gottfried (2012).
In this volume, you'll find the most extensive map study of the battle to date.5. A Field Guide to Antietam: Experiencing the Battlefield through Its History, Places, and People by Carol Reardon & Tom Vossler (2016).
Many fine Antietam tour books have been published over the years, but Reardon & Vossler's guide is both the newest and the best. The beauty and utility of its presentation, as well as the volume's breadth of coverage and depth of content, are all unsurpassed.