I would like one that has all the basic functionality of a basic "music" player including an equalizer.
The default media player in N900 is fine except it doesn't have an equalizer.
I also prefer to manage my music by just folders / filenames whenever possible.
the biggest problem of the internal media player is its horrible performance...sometimes its so incredible slow...a smart and simple, but fast music player would absolutely awesome
It would be nice to have functionality to restrict the music/media files search paths. For example, the builtin media player adds everything from the whole device (internal and external flash). I have some ScummVM games with soundtracks and those files would be nice to restrict from appearing in media library.
I am with jakiman the standard player needs some kind of EQ (atleast bass boost) it sounds great to me when using my Ultimate Ears earbuds because they seal tight and isolate all noise but when I tried to use my S9-HD the other day the bass was totally absent when on my sony phone I usually turn off the SRS on the S9's because there is too much bass.
I now use MediaBox as it has a MAFW backend which supports volume control while phone is locked. (Very handy)
Also has very intuitive playlist management and direct folder access. Doesn't use as much CPU as Symfonie either.