i would have to say 3rd gen. Although i dont own an iPod Classic, i have used one, and i do own the 3rd gen.
the 3rd gen iPods are just so cool with the all touch, lit up red 'buttons'. also no risk of damage on the buttons since there aren't any movable parts, except for the hold switch. 😀
ahh such fond memories with my first iPod 😛 i used it for a good 3 years before needing to get a new iPod