I particularly like string quartets, maybe a hangover from studying four part harmony in music school long ago. I already have a large number of string quartets, particularly from composers known for the genre: Haydn, Mozart, Beethoven, Mendelssohn, Schubert, Bartok, Borodin, Dvorak, Janaczek, Shostakovich, etc. I have some one off quartets e.g. Debussy and Ravel. I also have some not so well known ones e.g. two by Bax.
A while ago (pre-Covid) I attended a free concert by students of the Birmingham (UK) Conservatoire and I heard a string quartet by Grieg. My reaction was: I didn't realize that he had written one. So, I tracked it down on CD. I also started a search of other string quartets by composers who are well known but not for their string quartets. So far I have found: Fanny Mendelssohn, Tchaikovsky, Verdi, Rimsky Korsakov, Richard Strauss, Stravinsky, Ives, Prokofiev, Barber, Szymanowski, and even Rakhmaninov.
Of course, I can expand my collection with quartets by composers who are not well known at all e.g. I used to have one by Ruth Crawford Seeger but it was on vinyl and I have given away all of my vinyl; I should get it again. However, my priority at the moment, is for composers who are known but primarily for other genres.