This is a loaded question.
Unlike with most other genres, where there may be only one, or as many as a dozen or so recordings of a particular song or album, and then there may be a few different masterings of each recording, there are typically dozens of not hundreds of different recordings of individual classical pieces.
When talking about classical pieces, you get into the performance as a separate entity from the recording itself. A good example of this is the 1936 Pablo Casals mono recording of the Bach cello suites. The recording quality is pretty bad by virtue of the technology (and politics) of the day. But Casals' interpretation/performance is widely considered to be the best (or, at least top 2 or 3) by those who know about the piece, the history, etc. By comparison, the Watkin recording from 2014ish is respected as excellent in terms of performance and especially sound quality, but I dont think most folks would consider it a must-have. The Rostropovich version suffers from disappointing room resonances. The early Yo-Yo Ma version is well recorded but Ma hadn't really reached the level he later would and it's frankly a disappointing listen to someone who cherishes the history and significance of the piece. His more recent recording is said to be better but I have not heard it.
I picked that as an example because i spent 13 years playing classical cello and it's a piece that is dear to me (and all cellists).
Another example is rachmaninoff piano concerto no 2. Many believe that the composer's performance is logically the "most right" or "best" but it was recorded at a time where the SQ was abysmal by today's standards. There are some excellent sounding versions that have come out in the last 15 years, but some of them are... let's say... a bit self-indulgent on the part of the soloist, the accompanying orchestra, or both.
I own 5 versions of Scheherazade, 4 versions of The Planets, 3 versions each of Pictures at an Exhibition and Appalachian Spring, and 4 versions of The Pines of Rome. But in all cases, none of the pressings I own capture both the performance quality and sound quality that I desire. Thus, the search continues. To make things even more complicated, all of the things that apply to classic rock/pop/soul/folk etc albums in terms of different mastering, pressings and such can also apply to classical LPs. There are some Bernstein recordings that have been worked over numerous times that exemplify this.
I think the thing to do here is pick a few pieces you really like, then go explore some classical reviews of recordings of those particular pieces. You will find that classical reviewers very frequently spend at least some of their review addressing the quality of the recording as separate from the quality of the performance.
Gramophone Magazine has many reviews available online for free, and I tend to default to their recommendations. Unfortunately, they don't necessarily indicate whether a particular recording is available on LP, lossless format, or what.
Hopefully this helps at least a bit.... I would love to hear which recordings you land on in your quest. I'm always looking for good quality recordings of my classical favorites.
