After a long period of testing I think I can draw up some conclusions for myself.
The plugin is giving fantastic results these days, using this order of providers which I have found to be optimal:
4. Metal Archives (*)
5. Genius (fuzzy)
6. Deezer (fuzzy)
(*) only useful if you have a lot of (more obscure?) metal
To give some insights in the results I got during testing, here's a small sheet showing some results.
The test set contained around 250 songs that were matched with correct lyrics using Lyrics Reloaded with the above order of providers.
In the sheet the "100%" at the top represents these 250 songs.
The other cells show the success rates for individual providers and some combinations of them.
The test set was slightly larger than 250, of which about a dozen were not matched at all, or received incorrect lyrics.
Incorrect ones that came from Genius are at the bottom of the sheet.
(Deezer (fuzzy) provided many incorrect matches, but those didn't affect the positive outcome because Genius and Musixmatch would catch correct lyrics before Deezer (fuzzy) was queried)
Note that while 'Genius (fuzzy)' has a great success rate by itself, it will also provide a lot of incorrect lyrics when used as the sole provider.
(I saw incorrect matches rates well above 10% in that case)
To avoid that, Genius, MusixMatch and Deezer should always be set to come before Genius (fuzzy).
Thanks everyone that was and is developing and contributing to Lyrics Reloaded!
Time for me to stop testing now and sit back and enjoy ;-)