Alien invasion in movies: Aliens come to Earth and fight us ship to ship, human to humanoid. Leading man saves the race with a ragtag group of lovables.
Alien invasion for real, if it ever happens: Aliens put humanity to sleep from outer space, using whatever their way-advanced biochem tools may be, developed specifically for Earth humans. Something that won't affect the rest of the biosphere. Wait out of reach for best effect. Humanity dies off, blaming themselves for their own meddling in biotoxic warfare, never knowing what actually hit them. Aliens clean up as needed, take over planet.