The Top 10 'most honoured' speculative fiction novels are (in order):
Jonathan Strange & Mr. Norrell, Susannah Clarke
American Gods, Neil Gaiman
Handmaid's tale, Margaret Atwood
Prisoner of Azkaban, JK Rowling
A Deepness in the Sky, Vernor Vinge
Skellig, David Almond
The Yiddish Policeman's Union, Michael Chabon
The House of the Scorpion, Nancy Farmer
The Diamond Age, Neal Stephenson
Neuromancer, William Gibson
I have read, and liked, most of those. Azkaban is I think just the 'best Harry Potter' and not an all-time great book, but I think it is a worthy inclusion because of the impact of the whole sequence. Jonathan Strange is one of my favourite books ever. I personally preferred A Fire Upon the Deep to A Deepness in the Sky but they are both good books.
There are three I haven't read. American Gods and Skellig have both, funnily enough, been recommended to me by my children as books I should read.
The only one I know nothing about is The House of the scorpion. I'm wondering whether it was even published in the UK?