I do have some MP3 audiobooks ripped from Cassette and also some DAB Radio grabs converted to MP3, mostly comedy and radio drama.
Back when it was first released (around about 2012) I signed up to iTunes Match, matched up all my CDâs and MP3s and binned all the CDâs. A regret I still live with today.
Since finding Roon and Qobuz, I have replaced the majority of my iTunes music with Qobuz favourites or re-buying the CDâs, and matching them up in Roon (there was a lot of "group alternate versions).
I now only have 3 albums in Roon that are less than CD quality and thatâs because I havenât been able to find them on CD or any of the lossless streaming services.
I have a bit of a mixed bag, the vast majority of which is CD rips to ALAC or FLAC (about 70% of my 2000 album library). I still have about 300 albums in AAC purchased from iTunes over the years - I still buy the odd one that I canât get as a digital download or is exorbitantly priced on CD, and am always pleasantly surprised by how good this format can sound on my system. The remainder are 24-bit downloads.
The only things not lossless in my collection are live DJ mixes which usually only exist as mp3. Other than that no, lossless all the way.
I used to add mp3 but now I only add FLAC or dsf to my library.
While I have been a rabid audiophile since 1960 (i.e., when there is a sonic problem it doesnât just bother me, I feel physical painâwish I didnât), the content is the most important thing to me. And I have discovered that even acoustic recordings (i.e., pre-1926) sound significantly better in lossless rather than mp3. I keep mp3s when I can get nothing else for those recordings, and delete them when I have managed to get flacs. And every year the percentage of my Roon library that is flac = 24/>44 goes up. So great to be able to just delete the 16/44 files when they are bettered. And they are almost always bettered, but not always in predictable ways.
Only a few, all either because they were free with a vinyl purchase or, similar to another poster above, if they are bootlegs unavailable in other formats.
Michael
I have several mp3 albums, mainly from vinyl purchases. Boy, I love it when I buy vinyl and the download is available as a high res file (Mute and Erased Tapes to name a couple of labels which seem to regularly offer this) but all too often itâs mp3 only. I often add Qobuz versions for when listening at home, but keep the mp3 version in my library for Walkman or off-internet Roon listening. I really object to paying twice for the same albumâŚ!
At least FLAC. Lost half of my collection when I left iTunes but what I now miss I get it in Roon from Tidal 
!
Lossless whenever possible. If lossless isnât available, Iâll still take MP3. MP3 of something is still better than lossless of nothing (which would be lossy for your music experience).
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Exactly the same for me. If I like something and I can only have it in mp3, I listen to it, why not?
Everything else, lossless, alac or flac, mostly alac for Mac compatibility, ideally hi-res, plus some DSD.
No sure what value my post would add to this train of posts except for another response and the perspective included therein. Years ago, I digitized my entire multi-thousand collection of redbook CDs to AIFF format. Had I the foresight to have purchased a Sony PlayStation with SACD enabled instead of one that was not enabled, I would have converted my entire SACD collection. I even digitized all my DVD concerts or DVD audio albums. Titles that are no longer available except as a MP3 through iTunes (still refer to Appleâs program as) are also included in my music collection. All the downloads purchased over the years were either in AIFF format at the highest resolution and when available in DSD format 64 or 128, alas, my excellent W4S Dac wonât successfully playback 256. And for consistency, I employ BitPerfectâs DSDMaster to convert DSD purchased downloads to ALAC 352.8/24 so that I can add the album to iTunes despite employing roon for playback of the Native DSD versions. In my experience, my library of music in whatever format and resolution sounds very enjoyable. The only downside are pre-recorded music produced for reasons specified by the artist or by the engineer whose judgment resulted in a recording that is too hot (read shrill, metallic) and then I am obliged (or not) to correct digitally the poor recording. Hence, I find the many responses articulated in this thread that acknowledge music in a particular format lossless or not, that one enjoys is a reasonable perspective when the alternative is a piece of desired but unavailable/out of print. With roon set to upsample to DSD 128 and with a system that renders my collection in a highly enjoyable SQ, I find the musics the thing, the equipment seduces.
Richard
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This thread has the potential to separate the music lovers from the audio geeks.
I am nearly all lossless, but Iâll listen to anything that is good on whatever format Iâve managed to get it on versus not listening to it. After all, it always seems like the best music is recorded the worst anyway. There is nothing less inspiring than some iffy musicians recorded really well on some audiophile label.
I suspect we can all remember when we were young and really grooving to some music coming from a dreadful boombox or clock radio while getting ready for a date or a night out on the town.
Itâs all about the music, and getting closer to it.
Sheldon
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Not if I can help it. Almost all of my files are either lossless (ALAC, FLAC) or Hi-Res. I do have some albums that are a lot older that I have in AAC but nothing lower than that. I also have a subscription with Tidal for lossless for anything that I donât currently have in my collection that I want to listen to. My KEF LS50Wâs sure let me know when bad production and really lossy files are afoot.
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Sh*t! Weâre not supposed to do that anymore?
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I dunno, I put on a dance record and am dancing my lunch hour away listening to a Squeezebox Boom.
I only have hi resolution files (24 bit) in Roon unless they arenât available in which case I add the 16 bit lossless version. I never add anything less than lossless format - but I subscribe to Tidal and Qobuz so thatâs a luxury I pay for. If they donât have the album I want, I rip the CD from my collection of them (Joe Morello, Morello Standard Time is a priceless CD in my collection as an example).
In the end though, having your entire collection in Roon is fabulous in my opinion so whatever you can afford to put in it is worth it, imho.
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My digital library started life as CDâs on Meridian/Analogue.
When I went Meridian/Sooloos I ripped them all the CDs and sold them all. I exported the Sooloos library to native res. Flac and to AAC lossless (for the car).
When I switched from Sooloos to Roon I put my Flac library on the SSD in my Nucleus.
I now only acquire HiRes audio in Flac and stream the rest in Tidal. I donât own a file less than 44.1/16bit (Redbook) from earlier CD rips.
My iTunes library was always AAC and mostly based on CD rips anyway and that became the master for my car library.
The Roon/Flac + Tidal meets and exceeds my requirements.
What you play back on should also inform your decision. An unforgiving high-end system will take a lot of enjoyment out of your MP3s. But money spent on high res will be utterly wasted if rendered through $10 earbuds. If funds allow for it, your library should cater to the best rendering endpoint you have, or realistically expect to have.
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Only Flac and DSD. I have deleted my complete iTunes MP3 Scrap and ripped all again as Flac.
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My library for all practical purposes consists of lossless, except for a few albums/tracks I could only find in the lossy m4a/mp3 formats.
PS: I never sued my library