Syncing music with iTunes was so much easier than the junk sync apps that other players had.
(Granted, I don't use it anymore now that streaming services are so awesome. But I miss it like I miss the feeling of buying a CD and listening to it on the way home.)
Before I had an iPod I had a Creative MP3 player. The player itself was decent, but manually copying the files to it really was a pain in the rear end, especially when I updated metadata.