I don't think it's reasonable to try to pick one of these stories, for the reasons previously posted. Additionally, you should consider the fact that these stories were written at various times, and each really should be considered in the context of when it was written. Are the hopes and dreams of America the same today as they were in 1956 when Ginsberg published Howl? Or 1920, when Hughes wrote The Negro Speaks?

I agree with the second post here. Selecting one voice from the list to exclude or separate from the "spirit of America" feels like anathema to the American project. 

If the question were instead, "Which of these writers presents the strongest voice of political, social, or personal dissent from the mainstream American opinions of his or her era (or today's era)?" then I may be able to help you choose one.

However, dissent is not un-American. 

If forced to choose one, I would probably select LeGuinn’s “Schrodinger’s Cat” because she is really more of a science fiction writer and the story is just plain strange.  This is not to say that America is not about two contradictory realities, but given that I am not sure exactly what you are looking for, this one did not seem to fit in with the others as much.

I'm not trying to dismiss the premise of the question, but I think you would need to determine exactly what the "voice, the spirit, and the hopes of America" were before you began answering this question. While I haven't read them all, it seems to me that many of these books complicate the idea that there is a "spirit of America." Why would the voice of Langston Hughes or Allen Ginsberg be any less representative of "America" than any other?