I use farbfeld for all my image viewing, because compressing with gzip/bzip2 is good enough, and the "lel" image viewer works well for my use cases.

For videos, I try to put everything as webm, as from my experience it has a good quality/size ratio, when encoded properly (especially screencasts). I know that blind uses a raw format not suitable for storage, but some videos compressed with bzip2 might be "good enough". It can read farbfeld images natively too.

When it comes to sound though... I'm a complete noob, so I don't know much about existing formats. I think ogg vorbis is nice, so I use that, or mp3.

As for my opinion on these formats, well, simple formats make it easy to deal with. I've worked woth farbfeld too (got a few commits in xscreenshots IIRC), and blind obviously uses a raw format to make dealing with pixels easier. There is a really gokd reason for this formats to exist, however some format being maybe more complex are needed to achieve better/faster compression.

I just wished there was a format to concatenate music or videos with cat(1).