I figured this topic might generate some interesting replies. Someone had asked me about it in relation to strings, and I had also been giving it a lot of attention in regards to sound on our new instruments.
One thing I learned a long time ago, was not to try to make things "for the market". It's not that this is a bad idea for some people, it's just that I personally have always had a hard time nailing down where the market is. I always make what I like, and figure there will be others who like that too. Just the same, now that the designs are set, I thought to take a look at what people here had said about the topic. When I searched, I was surprised to see how little discussion had occurred.
The "depends" answers are the ones I like best - I put "Good or Bad" as the topic for simplicity's sake. Roy Smeck, for example, would probably go mad trying to play some of his stuff on a nice Devine or Compass Rose Tenor. He was more than a pretty good player, but not a fan of "slow".
Most of us are not playing Smeck style - nonetheless, it seems to me that there actually can be too much of a good thing. Tudorp gave an example of an instrument that I don't think could be played well through fast passages. There were references to damping - but again, that takes time.
Rick gave a pretty good description of our new instruments: "stiff sides & back - cedar top (though some will have spruce) - long sustain". The way we build our backs gave me the chance to dial it back just a bit. A long way from banjo sound, but at least out of the annoying aspects Tudorp mentioned.
There were some questions about strings, specifically nylon strings by Ralf. I do think traditional low density nylon strings are a good choice for lower sustain, and yes, I also think they tend to have a bit more of what I would call "meat" on them than flourocarbons.
We use nylons in some of our sets for the high note strings. If you are just buying varied diameters, one thing you can do with nylon, is fine tune your sustain. No other material changes more in this regard depending on tension. Give it some slack - get a nice sustain. Put some tension on it and you can make it drop dead in a heartbeat.