Nicest and favorites are, if you're only Sci-Fi including are: Alien
Blade Runner
Space Odyssey (2001)
All are good in different ways and mark a pivotal point in cinema and films.

1. ALIEN

2. Bladerunner

3. Heat

4. Dear Hunter

5. Jaws

6. The Thing (John Carpenter)

7. Terminator 1

8. 2001 S O

9. The Dark Knight Rises

10. Manhunter.

1. Prometheus AND 2001: A Space Odyssey (can't pick between them yet, until I see Paradise)

2. Fight Club -- Narrator's Haiku: "Worker bees can leave, even drones can fly away, the queen is their slave."

3. Bladerunner

4. Alien

5. American Beauty

6. Donnie Darko

7. True Romance

8. The Matrix (whole series)

9 Indiana Jones (whole series)

10. IM3/ DarkKnight series/Jurassic Park/ Peter Jackson's King Kong

I’m ignoring any Ridley Scott films on my list, otherwise it would be mainly a list of Ridley Scott films with room for very little else. Alien is still my favourite though.

1. Event Horizon

2. The Day the Earth Stood Still ( I do actually like both versions)

3. Predator

4. The Book of Eli

5. The Thing (John Carpenter)

6. The Keep

7. Final Approach

8. Phantasm (whole series)

9. The Matrix (whole series)

10. Dark Star

These stick out for me at the moment, but I could think of quite a few more that I would consider classics

1) Memento/ Prometheus (Don't make me choose- I won't do it!)

2) The Count of Monte Cristo

3) V for Vendetta

4) Moon

5) Let The Right One In

1) Alien

2) Prometheus

3) Star Wars

4) The Empire Strikes Back

5) Return of the Jedi

6) The Thing (1951)

7) Revenge of the Sith

8) The Terminator

9) The Silence of the Lambs

10) Manhunter

Does it have to be just films? There are so many great stories and universes from all maner of genres and if you don't mind mine are

1) Prometheus 

2) Mass Effect 1,2,3

3) Dead Space 1,2,3

4) Guyver series

5) LOTR and The Hobbit

6) The Elder Scrolls series

7) Aliens

8) Deus Ex

9) Babylon 5 series

10) Halo 

11) Avitar

12) Newer Star Trek

13) Star Wars

14) Pandorum

 15) And Many More

It doesn't has to be sci-fi films. I'm a big sci-fi fan thats why there so many in my top 10. Hades Infernal --> you mean video games right? ;-)

If you want you can write interesting stories in this discussion. Better you start a discussion only for sci-fi stories. :-)

There are some sci-fi films in your lists which wake my curiosity.

Heres my favorite top ten movies of all time.

1.Prometheus

2.Stargate the movie

3.The Thing

4.Apocalypto

5.Predator 1 and 2

6.Batman Begins, Batman Dark Knight, and the Dark Knight Rises

7.Alien

8.Star Trek and Star Trek: Into Darkness

9.Aliens

10.Immortals

@ 123Engineer

Yeah I'm all about the sci fi ,its always the first genre I check out.

With Video Games and movies they seem to be bluring into each other . The in-game cinematic or in-game movies are wonderfull to watch with you left to act out the next part and become part of the story .

I have been to see movies at the cinema that have vote buttons which determine what path the movie will take next , thats why I felt the need to add Video game titles to the list because in some ways they are interactive movies and they also spawn actual big screen movies too.

Just wondering , which sci fi films waked your curiosity?

I have seen most of the sci-fi films in your lists. I haven't seen Dark Star yet. Dan O'Bannon wrote the script for it and then for Alien. So it could be a film I have to see. Event Horizon, Pandorum and Memento I also haven't seen yet. 
Never heard of interactive movies you've wrote but sounds interesting. 

When I was younger I went on holiday to France , to a place called Futuroscope and thats where a saw the interactive movies . Its a whole theme park devoted to cinemas , you sholud check it out 

http://en.futuroscope.com/

Yer memento and event horizon deffinetly worth a watch at least once - memento can be watched two ways as well its very clever in that sense the chapters are organized on the dvd to play in a certain order when you first watch it and you can then watch it in another order as an easter egg - I wont say any more so as not to spoil it. 

I am a big game player as well but I have to say the best video game story line dont come close to the best film story lines for me. I think even with the games looking so good stroy lines are a last thought for many games. I just played the walking dead and it does have great characters and good story lines but it does feel kind of pointless that you have the game part to it as your choices never toatly change the story line you always come back to certian checkpoints as it would be impossible to make a free roaming storyline like that - that you could go in any direction (too much work)... stargate teh movie whoa that made a top ten  :O !

If i had to rate the best game story lines I would probably put dead space at the top at least in one and two three was a bit same old but quiet good. I would give dead space a 7 for story line vs films as a game story line its very good - the best but just lacks the depth of a films story line.

heres mine any way:

1. alien / gladiator / the sea inside (mar adentro) yes I put three but its hard to choose the top one! I like them for different reasons.

2. starwars (4,5,6)

3. Zatoichi (2003 version)

4. star trek first contact

5. aliens / star trek (2009)

also love terminator, predator, Indiana Jones, (titanic ahem! :D) and many many more - watch far too many!

anyway...another movie worth a look at : moon (2009) by david bowies son (edit: I see its one one persons list whoops...) Anyway just check it - im checking out tangerine dream version and dark star as I have only seen bits - hard to get hold of nowa days but there are ways...

Just remebered another great film from back in the day, Saturn 3

Have you seen 'The Time Machine' (1960)? It even won an oscar for Best Special Effects and it was nominated for an Hugo Award. It was filmed more than 50 years ago but it's still nice to watch. 

@Hades Infernal 

I like posters which are drawings. Makes me more curious. Never heard of that film so I'll look for it to watch. 

Yer Saturn 3 interesting but not a classic same with time machine... Reckon forbidden planet is the best oldy. 

Playing this game at the moment really nice atmosphere and story line for a game : http://facepalmgames.com/the-swapper/

@123Engineer

I love the original time machine , it is a timeless classic and one for the collection . I have'nt seen it in years .

@ djamelameziane 

The Swapper looks pretty nice , I do have steam and will have to take a closer look .

I was also thinking Akira, love the art work in that film , 12 Monkeys and Fith Element 

District 9 and Defiance series.

I have never seen Brazil anyone know if its worth a watch?

1.Alien

2.The Lord Of The Rings (all 3)

3.Jurasic Park

4.2001

5.Blade Runner

6.Prometheus

7.Pan's Labyrinth

8.Interview with a Vampire

9.District 9

10.The Fifth Element