Which writers do you think will be best remembered 100 years after their death?

Which writers who are alive now?

Margaret Atwood would be remembered for "The Haidmaid's Tale".

Barack Obama wrote a couple books. He will certainly be remembered. Bob Dylan won a Nobel prize for literature. I think his odds of being remembered are pretty decent.

As for traditional fiction writers, that's pretty hard to say. There are countless historical examples of writers' reputations rising and falling with fluctuating public tastes and intellectual trends. Your guess is as good as mine. 

Popular fiction writers usually fade from public consciousness within a hundred years after their deaths. I don't think people will be reading King, Rowling, Grisham, etc., much less doing research papers on the societal impact or underlying themes of their oeuvre.

The writers who will be remembered will be literary fiction authors. Margaret Atwood, mentioned in your first answer, seems quite likely.