The main reason for collecting different formats are the idiosyncrasies of each and less the sound quality. Vinyl satisfies an artistic need, since cover art is made more central. The coloration of records just adds to it, too. Vinyl also has the whole analog thing, which lets you hear each speck of dirt and crack in the record, which differentiates the experience from digital sound.
CDs stand out less because they have everything a full record has, except smaller. The music is digital, so they only ever get listened to in cars with CD players. A select few people, though, actually used the CDs capabilities in interesting ways. There was a time when people started tacking on programs to the CDs that could be accessed from the computer, like The Residents with their Gingerbread Man album.
Cassette and 8-Track have low quality which emits a pheromone that attracts lo-fi nuts.
The advantage of digital formats is the portability. They lose extra features and functionality, but they're really convenient to work with. The highest quality files are found in FLAC format, which can be lossless. The thing with sound quality on digital formats, though, is that at around a bit rate of 256 kbps is when the human ear stops being able to tell the difference in sound quality from an analog signal.
More often than not, the format is not what affects the sound quality, the speaker is.