Originally Posted by tore

I honestly don't think you'll hear much difference so if space is an issue, go with a space-saving option. If you have very good ears, you might hear a difference with your Sennheiser headphones on, but nothing that will really decrease your enjoyment of the music (even if you think you can hear a difference, that doesn't mean you, in a blind test, would be be able to clearly identify one as having a lower sound quality).

Just whatever you do, don't convert from a lossy source to another a lossy format. So don't convert f.ex 320 kbps MP3s to AAC 256 kbps. If your source is MP3 files at 320 kbps (rather than f.ex a CD), let them stay that way.