I kind of feel like the first rendition of The People in Your Neighborhood, with a fireman and a postman, is the signature, definitive, "go to" version of the segment, and yet at the same time, it seems like it's not.
It is the version they often take clips from when representing it in a retrospective, and it is the version used on the many albums (even if it's completely rerecorded). But then again, the full clip doesn't get a lot of exposure. It's only been released on home video once, while many of the other versions have officially been uploaded online (I won't get into how often episodes with it or others have been available). The rendition of the song in the 50th anniversary special also reflected a different version, the one with the grocer and doctor, even having the same opening dialogue.
But yet as I've checked "what links here" on the wiki, the first version has aired in more episodes than any of the others, with 18 appearances, though that's not too much more than the second-most-aired one (which I think aired in 16 episodes, I forget which one it is). Many People in Your Neighborhood segments from about the first three seasons aired in around 15 episodes each, while many of the segments from the late-1970s and early-1980s only aired around five or six times (there is one that I saw aired in only two episodes, I forget which one).
Of the four from the first season, the one with the dentist and bus driver aired in the least amount of episodes (I think five or six), while the rest aired in more than ten episodes each. And yet the dentist/bus driver remake from the 1980s is the '80s People in Your Neighborhood segment to appear in the most episodes for the '80s (I forget how many episodes, but it's the only one from the 1980s to air in a double digit number of episodes). That was the second to last classic insert of the segment, I wonder if the fact that they remade one with the same two jobs is what led them to stop doing new versions of the song (though the previous ones were hardly shown after), or if they were considering remaking older ones to avoid showing the adults when they were younger (which they obviously didn't, though this one aired until season 25).