Which of these Faulkner books should I read first?

I own Sanctuary, As I Lay Dying, and The Sound and the Fury. I've heard the last two are really difficult books. Is this true? I've always wanted to read him. I'm reading a lot of American literature lately to prove that my country has good authors too. Currently I'm reading Vonnegut and I just finished Gravity's Rainbow recently. What other books should I look into by him? Also if it is difficult try your besst to explain why they are. Thanks in advance.