The newest Sharp music player (initially for the 3000) is by far the best looking of all MP3 players, but it's limited by support (as in, you're lucky to get it play anything that isn't MP3) and stability.
Kino 2 over an mplayer base exhibits too much weird behavior for me to find it at all useful. Flickering toolbars, painted screen. So I stick with zplayer (also over mplayer), which handles just about anything I throw at it, organise playlists, and can read basic MP3 tags. The only minor drawback is browsing and spontaneous listening: everything has to be added to a playlist.
To put it briefly, then: I use
zplayer. (Looks like there are lots of new testing versions to play with!)
I would kiss the feet of the developer who could create an MP3/OGG/AAC player for the Z that could reliably read IDv3 2.4 tags and display cover art. But I think that's asking too much.