I voted floppy disk, but MP3 players were a pretty great advancement. My first could only hold about 20-30 songs because storage was still horrible back then, but the fact that I could swap out what I was going to listen to while going out to skate was just fantastic.
Now that I can fit thousands of MP3s on my phone but just use a streaming service.
Not sure how this isn’t the cassette player. Never really enjoyed carrying a walkman-sized CD player around, and cassette is the only way you’re listening to analog music on the go… unless someone knows of some weird mobile 8-track player I’ve never seen. But then have you looked at the selection of what was released on 8-track tape recently? So still no.
There is something to be gained by being nearly forced to listen to an entire album, in order, over and over.