I'd show them V, though that's a series (new one, I never saw the original). It would show them that no matter how good they appear to be or are, humans will react to them in every way possible. We're a complex species, ranging from extreme distrust to blind devotion and everything in between. Some of us will fight to the death, and others will want to become slaves. In fact, we'd probably be in the midst of a global civil war as they'd be watching it.
Imagination will often carry us to worlds that never were. But without it we go nowhere. - Carl Sagan