I don't know the latest models, but six months ago (when I bought a Sony DVD player) Pioneer and Sony both had a onscreen menues for mp3 playback, but only the Sony could display more than 8 caracters on directory and track names.
8 caracters is not much when you organize tracks in the format "track number - track name"
Example: "01 - Love for sale" will be displayed as "01 - Lov"
As I don't want to turn my TV on every time I want to browse an MP3-CD, I have printed a list with the album (=directory) names and numbers, so I can go directly to an album by typing it's number.