I don't like the fact that one might get left behind.... They were all too good for that....
However, if one of the last three must, I would personally think of Volume V, Wolves of the Calla. Other than Volume IV, Wizard and Glass, that was the only volume I had difficulty getting through, and at least the earlier volume struck me as having greatness to it even if I didn't enjoy it more than the previous volume (a first).