I'm not as well-read as I should be, but my favorite writers about music would probably be Glenn Gould, Leonard Bernstein, and Charles Rosen. The first two are certainly best remembered as legendary performers; in Gould's writing, it's his one-of-a-kind quirkiness that I adore, even if he often resorts to being "clever for the sake of being clever." With Bernstein, it's the sheer inspirational fervor that jumps off the page, even when the page is a television script.
Rosen, also a performer of the first rank, is the most legit scholar among the three, but the quality I value most in his writing is the same as what I find in Gould and Bernstein - the sense that everything he writes comes from inside of the music. Now that's a pretty vague claim, and it will sound like I'm putting down other musicologists, but I just mean that all three have an extraordinary way of getting to the heart of the matter that I believe comes from their genius as performers.
Rosen just turned 80, and this recent NY Times profile (too short) makes me feel incredibly lazy. He's still practicing three to four hours a day, with a performing schedule and repertoire to match. I also learned, and I say this with respect, that he's beginning to look a bit like Yoda. That's somehow appropriate, given the ease with which he dispenses insider wisdom. For example:
[Rosen] describes “recording fright” as “worse than stage fright,” from which he still suffers. With stage fright, he explains, you start out a little frightened, and then it wears off, but with recording fright, you start out fine and then grow worried.
I'd say that's exactly right. Especially as a collaborative pianist, there's nothing more stressful than getting towards the end of a "good take" and fearing I'll blow it, whereas once I'm into a live performance, the terror tends to fade away.
It's been far too long (perhaps as evidenced by my Haydn problem) since I read The Classical Style, but from both The Romantic Generation and the much less formal Piano Notes, I've learned so much about the special qualities of the piano and the composers who mined its deepest potential. Soho the Dog recently found an amusing quote from a flutist who, speaking of the composer John Adams, said: "I sometimes wish he’d date a flute player just so he’d find out how hard his music is to play." I don't know anything about Adams' flute writing, but I do think the importance of composers understanding the instruments for which they write is significantly underrated. Furthermore, though I'll admit to being biased, the piano is surely the most difficult to understand from the outside.
Not surprisingly, pianist-composers understand it best. Rosen writes, "Chopin and Schumann, above all, arranged the accompanying harmonies to make the notes of the melody vibrate." (p. 37) That statement seems simple, but the art it describes requires a very intuitive sort of sophistication on the part of composers. (Incidentally, it also explains why digital pianos are often so unsatisfying, and why the PianoTeq approach offers some hope.) Anyway, Rosen's ability to articulate what makes the great pianist-composers tick surely comes in part from his own mastery of the keys. Clearly, the Force is with him.