I havn't used either of those, but if you want a hard drive based I would recomend the Rio Karma. It can transer files over a network, so there is no need for messing with USB. It can play mp3, ogg, and flac. The only requirement to run it on linux is java. The application to transfer files over the network is a java app.
Sorry I can't comment on either of those players listed there, but I figured this info might be helpful to someone.