Since I re-watched "TNG: The Measure of a Man" lately, that probably makes it the episode I've seen most often.
Though there might've been a couple others I've seen 3 times.
Not much, 3 times, I know, but I like to wait until I've forgotten most things a show/book/game before re-watching/reading/playing it, and that process takes years.
Anyway, the Measure of a Man: such brilliant writing, so many different themes running throughout and such perfect acting to service the script.
That kind of thing is what got me into Star Trek, not the sci-fi setting, but the quality writing and allegories: such commodities were rare on TV at the time, they're slightly less so these days.