What defines “top”? Always so subjective…
“best”? in terms of the writing, the acting, the direction?
“the one I most enjoy rewatching”?
“the one I think makes the most powerful statement”?
There are even more possible definitions.
The 5th Element is a good example. It is science fiction only because it has a future setting. It could just as easily be considered a fantasy rather than SF. Buckaroo Bonzai is another good example, as is discussed above (and how the HELL have you not seen Buckaroo Bonzai?! I am taking away your nerd card and ripping it up!.
Dune is certainly not a great movie, but I think as it has aged it is more appreciated than it was at the time.
Terminator is not a great film either, but I’d argue it has had the greatest cultural influence of any film on that list (you could make an argument for Jurassic Park for that title though, and Back to the Future too). Matrix, on the other hand, has had the most influence on future movies.
I would probably say Brazil had the greatest impact on me as a viewer. And 12 Monkeys may be the “best” film on the list.