Faulkner may have chosen to end with a more coherent voice, because the last chapter ends in the present.  The previous chapters all lead up to the events of the present, and the eventual collapse of the Compson family.  Even though there are elements from the present in all of the chapters, they focus more on how the past has influenced the present.  Dilsey's chapter shows how all of  the past experiences talked about in Benjy, Quentin, and Jasons' chapters lead up to the end of the Compsons and the end of the Old South.   I am pretty sure that Dilsey's chapter is the climax of the book:

Faulkner's choice with the narrators of the chapters has an enormous impact on how we read the book.  Benjy's chapter is just a giant mush of memories and sensations, which is sort of how we remember the past as children, which is basically what Benjy is.  Then Quentin's chapter starts to clear up some of the things in Benjy's chapter, but it raises new questions about what really happened.  It is very surreal, much like things that we remember just having happened a couple days ago.  This is pulling closer and closer to the present, and the climax.  Then comes Jason's chapter, which is very plainly stated, and in my opinion, sort of boring.  But I think Faulkner intentionally chose to write it this way because it comes even closer to present events.  It is like someone telling a story about something they just did.  And finally Dilsey's chapter, which has really rich imagery and sensory detail, because it is most in the present.  I think Faulkner wanted the reader to feel like they were there with Dilsey at that moment, and his words help the reader to visualize what is happening.

Looking back on the book, I would say my favorite part was the entire experience after finishing it.  I was not really enjoying the book until I could look at it as a whole when I had finished.  When I was done with Dilsey's chapter, I realized what Faulkner was doing with time by having the narrators split up the chapters, and the book started making sense to me.  I didn't understand this until I was done.  Now I would say that this is one of the most interesting books I have ever read because of the way it was written.  I think that Faulkner was really innovative, because he perfectly captured what time is like, and memories.  This ties along with the meaning of the book.  I think Faulkner shows the effect that time has on memories and people.  In a way, he proves that time isn't just a linear thing, but something that can make someone's life completely unimportant in a millisecond.  Faulkner showed this by telling the story of a family and a culture that is falling apart, but he tells the story as a person would have lived it.  His story doesn't just have a start and an end, because everything that happens is connected.  He did prove that time can make a life, or a family, into nothing.