You might want to look up the old treatise on this by Walt Jung and Richard Marsh that was in Audio magazine a zillion years ago (OK, 37 years ago to be more precise). They addressed dielectric absorption and dissipation factor and how they affect the performance of the cap.
http://www.reliablecapacitors.com/pickcap.htmThe upshot is that from their technical standpoint Teflon, polystyrene and polypropylene float to the top, along with the seldom seen parylene. Polycarbonate was considered a second choice, and polyester was pretty much called rubbish.
Since then there have been a shit ton of subjective opinions published, and even more sales pitches. Mine are as worthless as any, and here they are -
Teflon film and foil tends to float to the top for me. Best resolution, but a long break in period during which they can sound pretty lean and thus a bit harsh. Once you get past that they really get out of the way of the music. Bring lots of money and make a very big chassis to hold them. Metallized Teflon, in my experience, sucks. Harsh, no matter how long you try to burn them in.
This sonic trend trend towards preferring film and foil over metallized film tends to carry over into polypropylene caps too. PPs are are my close second choice, all purpose caps and much more cost effective than Teflon. For some reason metallized film sounds much more OK in PP than Teflon. I don't know why. Thus you see a lot of them in our products. Regarding foils, tin foil seems to sound a bit more mellow and balanced than aluminum. I usually like PP film and tin foil caps a lot. Copper is more mellow too, though I need to listen to more of it as I think sometimes it gets a wee bit sluggish but I don't have enough data to be sure that is always the case.
Polystyrene caps typically sound very clean and clear. We are usually only talking about tiny values here, as the bigger values don't come in high enough voltages ratings for use in tube circuits.
Oil caps tend to be very un-harsh. In some cases too un-harsh, sounding rolled off or lacking transient attack.
Combinations, like polypropylene in oil, tend to sound like you would guess, a combination of characteristics.
Then there's how the layers are wound, what kind of leads are used, etc., etc.
Like an awful lot of stuff in audio, I think one needs to be careful to distinguish tonal balance from actual resolution. There are an awful lot of audiophiles who seem to prefer a somewhat unrealistically bright presentation, calling that "detailed". Yup, you hear more transient stuff if you turn up the treble and you can use a cap to do that. IMO it's kind of a beginner's mistake. For that reason I am pretty much a stickler for using the term resolution rather than detail. For me resolution is more of a notion of digging out subtle low level cues from the musical presentation that are enhanced by a good component without disturbing the tonal balance.
