Just to add one thing: The Shuffle can't play lossless formats and is "out" if you are looking for the "best".
Also if "best audio quality" is what you need then you are likely driving some high end headphone or stereo gear. If you are using earbud style phones then those are the weak link, not the iPod.
It depends on the earbuds you're using. If you've got a pair of high end Shures, that's a different story.