Favorite finish for speakers
If the speakers are entry-level, inexpensive, or ones I would be likely to replace with room changes (or if I had unlimited funds to change my speakers for decor-driven reasons), then a nice rosewood or mahogany.
If, on the other hand, they are speakers which I will probably keep for a long time, then gloss piano black, as it is classic and can be incorporated into almost any decor. Black has a higher long-term WAF.