Technology before brand.
There are two main types of quality caps: metallized, and film-and-foil. The former are cheaper, the latter better: by better, I mean smoother, more refined, more detailed.
Dielectric thickness doesn't matter very much, but metal thickness does. Just about anything thick enough to be wound up on a spool is thick enough for sonics, but a deposited conductor is a different matter.
Construction is also important. The larger the capacitance, the more the cap can suffer from inductance. MIT Multicap have a connection scheme that minimizes this. Duelund has a flat pack topology which is just about optimal.
Polypropylene tends to sound pretty good, but compared to styrene, is dull. PTFE (teflon) sounds a little bright compared to styrene. Styrene is, to my mind, the most neutral of the conventional dielectrics. These are the films.
For metal, the best is one which connects easily (usually solders easily). Those are silver, copper, and tin. These are the foils.
Now to the brands. I have used many, and MIT are my favourites. Solen f&f are less expensive but less good in my opinion, except for their PTFE f&f, which are as good as anyone's. Relcap makes a good capacitor. For the very best sound, I use MIT RTX series, which is a styrene / tin capacitor.
YMMD. Hope that helps.
