My recent "listing" interests have shifted to classical music composers and their works.
As with canonical texts, the first thing about starting a list is defining the scope. In the broad sense of classical music, my personal interest is actually quite narrow. I never really learnt or listened much classical music composed from 20th century onwards (I could argue that there isn't enough time to form a canonical opinion, but I wouldn't because in music some status of being "classic" seems to happen much faster than for canonical texts). I tried but never really got to the point that I truly appreciate vocal / choral music, opera included. I am also pretty basic, and am not that interested in digging up great works that ended up not being popular (my last try in here is C.P.E. Bach - but decided at the end that his works are not popular for a reason).
With this frame, the number of composers that matter are really limited! Especially if we exclude composers with really just one popular piece - like Pachebel, whose canon in D is pretty good music, but even the Gigue in the same piece is almost never played. And the current understanding of western classical history is pretty central European (German) biased (especially against southern Europe - Italy and Spain). So the list of instrumental composers that truly matter in the 18th and 19th century comes down to, in chronological order of great works composed:
1. J.S. Bach - I really never like Bach in any real sense, but any instruments I learn I can't bypass him - violin (Sonatas & Partitas), viola (Cello Suites), piano (Well-Tempered Clavier I&II). He is more fun to play, than to listen. And his music tends to be sad/negative rather than entertaining/uplifting - so out of his massive universe of works, the truly enjoyable ones I feel is only a very small percentage. Before Bach, it feels like pre-history - Corelli, Vivaldi, Purcell. Handel is mostly still in the concert repertoire for his Messiah Oratorio - since I am not into choral music, he is out too.
2. Mozart -- there is a generation of Bach's sons that is skipped. I can't find too many J.C.Bach's works to listen to, and C.P.E. Bach may have a bit of comeback these last decades, but I find most of his works not that interesting. The ones that I think have some potential is his cello concertos. Among this list, Mozart is the only instrumental master who also "made it" in the opera world. His Piano concertos I don't think have ever been really surpassed.
3. Haydn -- why does Haydn come after Mozart? Because Haydn's best / most well-known works nowadays almost all date from 1790's after Mozart's death. He is the father of string quartets and symphonies, but Haydn always feel like a little bit in need of "revival." He is solidly on my list because he is through and through entertaining, and most often uplifting.
4. Beethoven -- he is the central guy in the canon, but unfortunately I can't really seem to get myself to like most of his works, especially his late works that are supposed to be deep. When he wants to be charming though, he could be very charming - think Moonlight piano sonata, Spring violin sonata. My personal favorite is his Bagatelles Op.119.
5. Schubert -- I don't really listen to Lieder, so Schubert is handicapped from the get go on this list; and he is often sad and melancholic -- I give him a pass though as sometimes he is so beautifully sad (think the theme of Arpeggione Sonata). But just the instrumental works he finishes in the last years of his life are more than enough to place him solidly on this list.
6. Chopin -- he is one of the three non-Germanic composers on this list. He mostly only composed for piano, especially miniature piece. He knows rules of composition, but using those rules to create a completely different sound world. My only complain is that he tends to be on the melancholic side, that is what I always feel his prime are in the years of 1829~1834, to me his Preludes are already a hint too "dark." My you got to give him credit - it is hard not for anyone to not like Bach if the only Bach pieces one listens to are his Preludes from Well-Tempered Clavier Books.
7. Mendelssohn -- he may not be deep, but his music is charming. As a violin player, his Violin Concerto always hold a special place in my heart. (And not as sad as Bruch's!)
8. Tchaikovsky -- yes, you read it right, I flew by Lizst, Berlioz, Schumann. Can't say there are no good Lizst works, but the portion of enchanting music is so small compared to Chopin's. I never got to listen to Schumann's much. Every time I try somehow I am never impressed. Thus the jump directly to Tchaikovsky, his prime in my view are 1775-1880, a full generation after Mendelssohn's Violin Concerto of 1844. His most popular works, not so different from the last two on this list, are primarily symphonic, with some chamber music, and less solo (piano) music.
9. Brahms -- most of his works are too serious for me. But he revitalized symphony as a genre. I can't decide if his youthful works are better than his mature works, but in any case the center and apex of his opus has to be his Symphony #4, which is in the late 1880's.
10. Dvorak -- The most popular works today of this Czech composers mostly originate in his late period from the late 1880's through right after his expatriate stint in the United States.
This is it, my list of 10 composers.