Some people like CDE metal foil, expecially where low end is critical. For me, as long as they are mtel foil or metalized foil, big in size, they would normally be good enough for testing.
I just use wilmslow audios supersound polyprop caps when used with a good tweeter, they sound excellent to me. I cannot really justify using stupid priced caps in a loudspeaker unless someone wants to buy them for me.