Bryter Layter may be his best album even if it doesn't have a song quite as strong as River Man from his debut.
Today, emerged from obscurity, everybody seems to love Nick Drake. He's a tragic figure and died very young, which is of course interesting.
In my own music listening habits, he doesn't quite have staying power over large amounts of time. The mostly unspoken reason is his songs are nice, but also often a little dull
Between the two, Carole King is of course a lot more interesting. A true giant in music.