This one was tough. There are so many more that could have been added to the poll. It's tough for me to choose between Ghostbusters and Spaceballs. I never considered Ghostbusters sci-fi, but Wikipedia and imdb say it's so, and after thinking about it I guess it makes sense.

Marty McFly: [looks through a camcorder] This is uh... This is heavy duty, Doc. This is great. Uh... does it run, like... on regular unleaded gasoline?
Dr. Emmett Brown: Unfortunately no, it requires something with a little more kick - plutonium.
Marty McFly: Uh... plutonium? Wait.
[lowers the camcorder by his side and points to the DeLorean]
Marty McFly: Are you telling me that this sucker is nuclear?
Dr. Emmett Brown: Hey, hey, hey. Keep rolling. Keep rolling, there.
[Marty looks through the camcorder again]
Dr. Emmett Brown: No, no, no. This sucker's electrical, but I need a nuclear reaction to generate the 1.21 gigawatts of electricity I need.
Marty McFly: Doc, you don't just walk into a store and buy plutonium. Did you rip that off?
Dr. Emmett Brown: Shhhhhh. Of course. From a group of Libyan nationalists. They wanted me to build them a bomb, so I took their plutonium and in turn, gave them a shiny bomb-casing full of used pinball machine parts!

Wow, I was certain Ghostbusters was going to win this poll. But I'm a big Mel Brooks fan, so I'm very happy to see Spaceballs taking the early lead.