Ooh look a list!
These things are entirely subjective and so barely worth arguing over, but I can't remain silent on the topic of their tenth best science fiction movie:
You know what's a better SF movie than Back to the Future?
EVERYTHING EVER MADE BY ANYBODY EVER.
There are other weak links but this one's egregious, a Sesame Street game of Which of These Things Is Not Like The Others? featuring nine different breeds of cat and one naked circus clown. Blech.
I bet I can come up with a list of ten just okay SF movies that deserve to be on that list over BTTF. No classics allowed, just solid genre exercises that are more deserving of a spot.
Close Encounters of the Third Kind
Star Trek II: The Wrath of Khan
Invasion of the Body Snatchers (1978 remake)