Id say the iPod video 5th gen, or the ipod mini / iPod Nano 2nd gen. were the best. Some may argue the 5th gen had all the scratching issues, but I feel it was very solid. The Mini / Nano is simply a tank and if you dont have a large music collecting is simply bliss.
The Mini
Perfect size and weight. Solid aluminum chassis.
Easily USER replaced parts from batteries to screens.
Future-proof CompactFlash card connection allowing 32GB+ storage.
Battery life (if fresh and upgraded) of days.
Might not have color, might not be able to play games or videos, but its the BEST music player ever.