As far as iPods go, the first generation shuffle is king, followed by the 3rd generation iPod, followed by the first generation Mini, followed by the 5th generation iPod. And it's not because of the audio DAC, it's because of the headphone amplifier itself which Apple has *always* cheaped out on, hence the popularity of line out cords.
The first generation mini had terrible sound quality; compromises were made for its (at the time) small size, the 3G iPod was also mediocre. Sound quality improved significantly with the first gen shuffle. The worst of all though was the first iPod Photo, which could not play back solo piano without significant distortion.