I usually use ArkivMusic to search for and get the details of Classical Music releases - as (SA)CDs. If that fails, Primephonic usually has them; if not Presto Classical.
At a pinch I can even find something on Amazon. I’ve found Discogs for Classical music to be hard to navigate and MusicBrainz, which is preferred say by Paul Taylor and Jaikoz (not criticizing: I appreciate that they have their place!), hard to navigate because we do not think in terms of Artists, ‘Songs’ and Tracks.
Forum members have referred to AllMusic a lot - e.g. in another thread here.
How comprehensive and easy to navigate is AllMusic, please? Is it to be preferred for accuracy, comprehensiveness and ease of use for Classical music?
As @Mike_O_Neill says I don’t think you will find that allmusic is being referred to a lot because of any of these reasons. The main reason allmusic is being referred to is that it is the public face of the TiVo metadata supplier that roon uses. The reason for roon to partner with TiVo only roon can say but the result is that in the roon eco-system the naming conventions in allmusic can be considered a kind of defacto standard. If you cannot get an album or composition identification then often the easiest thing to do is find your album in allmusic and copy into your tags exactly what you see. That way you have converged your tags with roon’s own databases and make it that much easier for roon to make an identification.
I try to avoid doing this but some composers have very complex cataloging conventions (Ravel, Teleman, others) and there is no reason why your homegrown convention or whatever you copied off the back of the CD necessarily matches TiVO. Pragmatically, then converging your tags by cutting and pasting from allmusic may be the easiest and quickest thing to do.
I would imagine that roon sees that Allmusic catalogues nearly every release. Whether Allmusic has good metadata for every release is another matter. They are certainly dependent on what information the labels provide them and that varies greatly from label to label - just compare what information different labels provide in their liner notes. That said, Allmusic has not/does not consistently provide recording information (date, location) and you may not be able to figure out all the musicians if you don’t already know it (look up Schumann: Concertos for cello and piano and see if you can tell from their data which of Coin or Staier play which compositions - though I’m sure you know that Coin does the cello and Staier the piano). Even though it would be nice to have a single site with comprehensive information, it is often best to go to the labels own web site, though there is considerable difference between labels (over the years Universal has sadly downgraded the quality of metadata they provide on their site, for example - in my opinion Chandos and Hyperion set the gold standard for metadata).
A subscription doesn’t improve searching or the quality of the data you can access. It just allows you to use allmusic to rate albums and keep lists of various kinds. It’s more directed to pop music as one of the features is advance notification for when an artist is going to release an album.