Okay, “The Body” is just about the worst possible introduction to Buffy I can think of. It’s fantastic television, but it’s almost entirely unlike anything else in the entire series. Similarly, the gimmick episodes like “Hush” or “Once More with Feeling” aren’t great entry points, either. What you want is an episode that showcases all the facets of what made Buffy a great show. It’s got to be funny, with a touch of drama. It’s got to have some hints about the overarching plot, but not be so mythology heavy that it overwhelms the new viewer. And it should deal in the major themes of the show, such as growing up, the responsibilities of adulthood, and the stresses of being a teenager.
With that in mind, I submit the season three episode “Band Candy” as the best entry point.
“The Zeppo” is a close second, but is hindered by the fact that titular star of the series is barely in it. A good introduction to Buffy should focus on Buffy, not one of the supporting cast.