its quite possible that youll be better off with the mp3 player if all you do is put mp3s on some kind of media. I would go into size, but as we all know, the ipod is very small and quite a nice mp3 player. Downside of md right now is the lack of upload on net MD. This is available on that mp3 player.
well, if you do decide to get a MD player, make sure its net md (even thought net md sucks right now, youll need it of you have mp3s).