The Price We Paid: The Extraordinary Story of the Willie and Martin Handcart Pioneers, By Andrew D. Olsen, Deseret Book, SLC, Utah 2006.
In my opinion, this is the best book dealing with the Martin and Willie Handcart Companies. He avoids the problem of combining the two stories, by dedicating chapters to each company and telling the story of when is happening in the journey. At the same time, some of those areas which have very similar stories, such as the conditions on the boat trip across the ocean, he tells in a single chapter. He does a good job of telling the conditions on the ship, and on the handcart trail. He also dedicates significant space to telling personal stories.He doesn't get lost by trying to combine the two stories. He also has significant historical background and has obviously done a great deal of research.
He does a very good job of describing the rescue, and the involvement of so many people from Utah, who came out to meet the struggling Saints.
The author devotes a significant portion of the book to tell individual stories. This is in two sections, the story of individual on the journey, as well as the afterward story; what become of people after they made it to Zion. This includes the stories of many of the rescuers.