Saitō Ryokū on the "noble, lovesick" koto vs the "common, lustful" shamisen (although the word he uses is "samisen", because he was straight out of Edo):

The koto is a flower, it admires other flowers: it is inviting. The samisen is a moon, it floats like the moon: it is provocative. A beggar pauses at the side of the road or at one's front gate: if he plays the koto, it rings with misfortune, one's thoughts turn to ruin; if he plucks the samisen, the song is one of vice, one's thoughts turn to decline.

"Think on the Mount Li of old...": this is a koto song. "When you stayed all through the night...": this is a samisen song. The aware of the koto is sought at leisure, and is at last concerned with another. The aware of the samisen is pursued in haste, and is ultimately about oneself.

Reverse the two, call the koto a moon: it is but a veiled and hazy one. Call the samisen a flower: it is brittle and dying.

(Of course, these are merely "miscellaneous impressions" that Saitō formed "in town" and "at festivals".)