The answers all seem very sensual and subjective. I don't know at all - certainly not about classical guitars.

I saw Ken Nicol (Steeleye Span's guitarist) give a seminar some years ago at Fylde folk festival. he said that cedar was his favourite because the closer grain gave it a 'punchier' tone.

I was so impressed with KN that I got myself a cedar topped guitar, however it availeth nothing, and I started getting compliments for the mellow tones that I got from the new guitar.

i should have thought though with a nylon strung guitar - the real choice is whether to get one of those that the flamenco players use - very thin cypress wood that they use to such advantage for that 'explosion' of sound. when then do that roll of the fingernails called a rasguedo.