Dark Side is a good choice since most issues of it have a great sound to it. But what I want to introduce people to is "listening" to music in general, moving away from music as background noise, and for that I think there is no better than Wish You Were Here. Vinyl for me is more getting into music than it is about sound. Because once you get into sound over music youre going down down down the rabbit hole. I have done this to 3 friends already and they come out of it with a new understanding of what music can be. Not individual songs or playlists on Spotify, but an album, a story, an experience. But first I like to ask what they want to hear.