Media Choice?

There's no one format that you can depend on for best sound.  Sound quality varies from album to album so much that how well the album was recorded is the most important factor in sound quality.  From there, how well it was converted to various formats varies also.  You have to listen to various albums in various formats on a case by case basis if you want to find the best.

You can find discussions of sound quality and formats here:

https://forums.stevehoffman.tv/forums/music-corner.2/

but it 's not easy to find the best sounding version of each album.

I also expect the sound quality of streaming to continue to improve because it's the dominant format now and will probably become more dominant as time goes on, but again, you don't own the music.

I don’t think there are enough HDCDs around that this would be a good option for building a collection.

Cds are generally cheap and plentiful right now so that’s a plus. However, many cds have been dynamically squashed. They are loud all the way through, no soft sections and loud sections. That can make finding good sounding cds difficult depending on your taste in music.

I think that streaming can sound as good as cds or better, and streaming appears to be the future of digital audio. However, you don’t own a copy of the music you stream, so if your streaming service disappears or removes certain albums or artists for whatever reason, you no longer have access to that music.

So I would try to find on cd the music you want to own and keep forever.  Buying downloads is also an option.

Resources for finding good sounding cds are the Steve Hoffman Music Forums and the Dynamic Range Database. Once you decide which mastering of a particular album you want you can find cds listed by mastering on Discogs, but check with the seller before buying because sellers don’t always list their cds under the correct listing.

I also recommend you stream because it gives you access to a tremendous amount of music, it sounds great to me and the sound quality will probably improve beyond cd as time goes on, and the scenario where you lose the music you want to listen to may not happen.