wkbdgeorge said:
I thought I read in another posting that someone liked a metallized polystyrene. Maybe I am mistaken.
Remember, these are very subtle differences, and in some circuit it is entirely possible metallized polypropylene sounds best. or the cheapest electrolytic you can find.
There is an easy way to solve this. Build a circuit, and start swapping caps. Maybe you won't hear a thing, maybe you'll find some caps work better than others. Caps are cheap enough so you can buy a set for just this purpose.
I have not seen any listening tests on this topic I would consider trustworthy, and I don't think there can be any. Not everyone likes the same things.