Holy crap what a lineup of heavy hitters. Any of these could have gotten my vote:
Hyperion by Dan Simmons
Dune by Frank Herbert
Do Androids Dream of Electric Sheep? by Philip K. Dick
Enders Game by Orson Scott Card
A Canticle For Leibowitz by Walter M. Miller
Paypal me $9.95 and I will tell you which I voted for
.