iPod all the way - it has the widest range of docks, and you can use MP3 files just fine.
They're prettier than everything else too, which my wife and daughter like.
Because they have the most accessories, you can get things like in-car charger/FM broadcasters - since I got mine, I've not used CD in the home or the car.
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Overhead, the Albatross hangs motionless upon the air,
And deep beneath the rolling waves,
In labyrinths of Coral Caves,
The Echo of a distant time
Comes willowing across the sand;
And everthing is Green and Submarine
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