Peter Grant (no link because it disappeared) had a page of Great Science Fiction Quotes in his blog. I can't pick just one as a favourite. Here are some:

“There’s no real objection to escapism, in the right places… We all want to escape occasionally. But science fiction is often very far from escapism, in fact you might say that science fiction is escape into reality… It’s a fiction which does concern itself with real issues: the origin of man; our future. In fact I can’t think of any form of literature which is more concerned with real issues, reality.” – Arthur C Clarke

“Isn’t it interesting that the same people who laugh at science fiction listen to weather forecasts and economists?”

“Science fiction writers foresee the inevitable, and although problems and catastrophes may be inevitable, solutions are not.” – Isaac Asimov

 

“Experience comes from doing, not from being told. Experiment and discover. Seek and find. It is not machinations of others that compel us to do so; it is our need to know. It is, in the end, the way we learn.” – Terry Brooks, The Talismans of Shannara

 

“A neat and orderly living space is the sign of a dangerously sick mind.” – Mercedes Lackey, The Black Gryphon

 

“Reality is the part that refuses to go away when I stop believing in it.” – Phillip K. Dick

 

I found a few others in my own searching:

"For me science fiction is a way of thinking, a way of logic that bypasses a lot of nonsense. It allows people to look directly at important subjects". - Gene Roddenberry

 

"Fantasy is the impossible made probable. Science fiction is the improbable made possible." - Rod Serling, creator of The Twilight Zone

 

"The mind is a strange and wonderful thing. I'm not sure it'll ever be able to figure itself out. Everything else maybe, from the atom to the universe, everything except itself." - "Invasion of the Body Snatchers" (1956)