There are some songs that seem to have a "good" repertoire, a "bad" repertoire and two "neutral" ones. Symphonic echoes is one:

Bards in a mood of sharp-wit are best able to master this technique, while
those who are overly brazen may find their style too straightfoward to
utilize this method to its fullest potential.

Comedic good, epic bad.

So for a bard with preferred repertoire romantic and an instrument that's equally good for all styles, would he be better off singing echoes in romantic to get his preferred repertoire bonus or comedic because that style is "good" for echoes instead of just "neutral"?

For the purposes of a particular song, instrument notwithstanding, you're pretty much always best off singing it in a repertoire that's better for it (i.e. moving from one that's neutral to one that's good, or moving up from bad to neutral).

Or to put it another way, the bonus for singing in your preferred rep is a small bonus; the bonuses for singing a song in a repertoire that is good/bad for it are almost always much larger bonuses/penalties.

Thanks! That's exactly what I was looking for.

By the way, am I reading the help file for symphonic echoes right?

It looks like the only song where the good and bad styles aren't polar opposites, in that comedic isn't the opposite of epic.

It's definitely anti-epic ("overly brazen") which would usually mean it's pro-romantic. But the comment about "sharp-wit" makes it seem pro-comedic instead.