I tend to think that the titles of the chapters should be tied into the themes or essential events of each chapter.  For example, chapter 1 might earn the title of "The Riverbed" because of the details offered of the small river in it as well as how George warns Lennie to return back there in the event of problems or concern.  The second chapter might be described as "The Quarters," as so much detail is given into where the men work and live as well as how much of the action happens there.  Chapter three would have to be "The Silence," reflecting the reactions of everyone to Candy's dog being killed and the waiting for the event to happen.  For Chapter 4, I think that "The Conversation" might reflect both the shared discussions that happen between Lennie and Crooks, Candy, Crooks and Lennie, and the brutal conversation between all of them and Curley's Wife.  I like the title of "The Tight Sausages" for Chapter five, reflective of how Lennie saw Curley's wife's hair and wanted to touch it because it was so "purty."  "The Decision" would have to be the last chapter's title as the decision to kill Lennie becomes the defining one in the narrative.