Temis the Bleeding Aorta wrote:
TOS was nonexistent and the less said about TNG's, the better.
"Encounter at Farpoint" is weak, but it sets up Q and themes that are active for the duration of the series, and introduces most of the character well enough.
As for the original series, both "Where No Man Goes Before" (the second pilot) or "The Corbamite Maneuver" (the first regular episode) are great at introducing the themes and ideas of the series. Outside of the big three and the guest stars, they're not much for introducing characters, but the original series was never that interested in those sort of stories.