Havin read "The Somme: Heroism and Horror in the First World War" by Martin Gilbert, "The Somme" by Robin Prior and Trevor Wilson, and "The Somme" by Lyn MacDonald, I found MacDonald's book to be the best of the three.
While Gilbert's book is a general history which provides a broad overview of the battle, it is not able to convey the movement of the battle. MacDonald's use of maps, as well as her step by step approach in describing battle is much easier to follow.
In addition, MacDonald lavishes the book with detailed accounts by survivors. It is not a rarity to find entire paragraphs, rather than sentence long quotes, taken directly from the individual soldier's words. This is incredibly welcome as it gives the reader a better understanding of what actually happened on the ground.
Prior and Wilson's book is great if one is interested in tactics. In addition, their book debunks several Somme myths which I will not go into here. Yet their work does not bring the reader into the lives of the troops or their experience outside of citing casualties.
MacDonald's book describes the establishment of the "Pals" battalions, their training and their general experience prior to the battle. In addition, she also discusses the role of the ANZAC on the Somme and gives an excellent account of their history from Galipoli to their attack on Pozieres.
While Wilson and Prior focus on tactics, Gilbert vacillates between tactics, general history and the soldier's own experiences. Wilson and Prior succeed in showing the immense planning, terrible cost and miscalculations of the battle, but fail to craft an comprehensive narrative.
While touching with its poetry and its frequent, tragic recitation of "he is listed on the Thiepval memorial," or "he is listed on the Gommecourt memorial," Gilbert's book does not make the battle more comprehensible.
MacDonald on the other hand gives a wonderful start to finish narrative of the battle in which she uses the survivor's own words to draw the reader in. In addition, MacDonald also discusses a variety of different roles from the soldiers to the Pioneer battalions to wireless operators.
Overall, while each book is worthwhile in its own right, MacDonald's is the best read for both the amateur and the historian alike.