What is the best science fiction story you have ever read?

Sixty Days and Counting by Kim Stanley Robinson There has been one more winter of wildly careening weather since the winter of Fifty Degrees Below. Frank Vanderwal is still working for the NSA, coordinating projects aimed at combating the causes of rapid climate change. With the election of Phil Chase as President, Frank and his co-workers' jobs are about to gain in influence and importance. Charlie Quibler, Frank's friend, is pulled away from working part-time at home and raising a son to being a full-time science advisor to the President. Frank's new love, Caroline, has gone underground, pursued by the same black ops organization whose plans to fix the election Frank and Caroline helped thwart.

My favourite SF book is Starship Troopers by Robert A Heinlein. If you have only seen the movie, don't let that prejudice you against the book -- they are NOTHING alike! The novel follows the career of an infantry soldier in a war between Earth and an aggressive insect-like alien species. That much is the same as the movie. The book, however, focuses on Earth's society, the form of government that has evolved, and WHY the main character became a soldier. The war is definitely a subplot -- not the main plot.